By the end of the game, they had seen their team earn another important win. In addition, the performances both on the pitch and in the stands will surely have strengthened the bond between United's players and the club's fans.
With the travelling Red Devils in superb voice, here is the story of what they sang and why. Not-safe-for-work language has been replaced in square brackets to convey the meaning of what was being sung.
A little over half an hour before kick off, the first hint of a chant was heard from the away fans who had gathered in the ground early. A group of three or four, positioned just about behind the goal, began chanting David De Gea's name as he warmed up.
Full of enthusiasm, they attempted to drown out Tony Pulis' pre-match press conference, which was being played over the public address system at significant volume.
Their number grew to around 10, congregated in front of a One Love tricolour flag.
Within five minutes, the PA system had paused to read out the teams. Zlatan Ibrahimovic's song spread to around 40 or so of the gathering Reds.
As the atmosphere in the stadium began to build, a West Brom fan was interviewed on the pitch. The United fans had found their voice in earnest by this point, with their end full with 15 minutes to spare before kick off.
It was a classic selection as "U. N. I. T. E. D" and "The Banks of the Irwell" were followed by an extended rendition of the "United Calypso," all blasted out over the loud electronica with which the Baggies built up to the match.
A raucous group of Albion fans—accompanied by a drum—took up the other half of the Smethwick End, in which United's fans were located. Despite that, and in spite of the ever more bombastic pre-match soundtrack, Henrikh Mkhitaryan's song and another round of Ibrahimovic chants were still audible.
The final announcement of the teamsheet was met with rapid chants of "United! United! United!"
A traditional rendition of "Hello! Hello! We are the Busby Boys" followed kick-off. This is almost always sung near the beginning of games and is then peppered throughout.
With the unpleasant lyrics, "if you are a [Manchester] City fan, surrender or you'll die," it is a holdover from a different age of travelling support but is still used as a statement of intent.
Shortly afterward, West Brom fans began singing "We're the Albion," a chant that was greeted with an enthusiastic airing of "Viva Ronaldo" from the away fans given both are set to the same tune.
A core group of United's support took up a round of the "United Calypso" during an early period of promising Albion possession.
Perhaps the fact it did not quite take off could be put down to nerves. However, when West Brom supporters again began to sing their version of the omnipresent "we're the [insert club name here] boys, making all that noise," of course "Viva Ronaldo" began again. If the West Brom fans were going to use that tune, that was always going to be the response.
Then came a blast of delirium, as Jesse Lingard's excellent cross was headed in by Ibrahimovic. "United! United! United!" came the cry with synchronised fists pumped in the air. Then, as that settled, Ibrahimovic was treated to yet another rendition of his song.
"Who [on Earth] are Man United," rang out. This less than family friendly version of "Glory, Glory Man United" was co-opted from rival fans' adaptation of the original lyrics. As United became more and more successful, the notion that anyone would not have heard of them became ever more ridiculous.
The gleeful irony was embraced by United supporters, who stole what was designed to be a taunt for their own and made it a celebration of their notoriety.
Then came first "20 Times," then "Hello! Hello!" again. The goal inspired an already excitable crowd, and the noise was to be unrelenting for almost the rest of the game.
Of course, this being the Christmas period, it was only a matter of time before the first airing of the "12 Days of Cantona," with the extended "five Cantonas" as always the highlight.
When West Brom fans made unfavourable comparisons between United and Manchester City, the Red Army responded with the ever-popular "You've Only Come to See United!"
One of the universal features of United away ends is the aforementioned "United Calypso."
This throwback song, with its lyrics invoking the Busby Babes and containing the following quaint instruction, "whenever they're playing in your town, get yourself to that football ground. Take a lesson. You will see the football taught by Matt Busby and Manchester, Manchester United," feels almost anachronistic in the contemporary football landscape.
But it is a pure expression of football joy and pride in a team's ethos and tradition. It will often be sung when the crowd gets a little quiet. Here a small group began singing it and kept going for a couple of solid minutes before the bigger group joined in. It lends itself to repetition, and the moments when it catches fire are some of the most enjoyable to be a part of.
On the 20-minute mark, it was time for chorus of "United Road," at least the 15th different song or chant heard. The 16th followed on its heels, as "Oh, What a Night" began. This paean to the 1999 Champions League final has become immensely popular over the past couple of seasons.
A Wayne Rooney shot was saved on to the bar shortly thereafter, and both the chant of his surname and his "White Pele" song got immediate airings. Ibrahimovic then committed a heavy foul on Craig Dawson, for which he was booked by referee Anthony Taylor and serenaded by United fans.
Another recent favourite was heard after 25 minutes.
The version of "Spirit in the Sky" with lyrics adapted in praise of George Best is not quite as ubiquitous as it became at the end of the 2014/15 season and the early part of last season, but few games pass without it being heard.
The older, more traditional Best chant, "We All Live in a Georgie Best World," to the tune of "Yellow Submarine," followed immediately. It was nice to hear the classic had not been forgotten in the wake of the more recent hit.
When the Albion fans sang "you let your country down" at Rooney, United fans responded with "world champions twice. Once more than England—world champions twice" and another song about Cristiano Ronaldo, with its lyrics critical of England. There was then a song with unprintable lyrics about what the Albion fans—and the football world in general—could do with England.
A pocket of WBA's supporters responded with a brief burst of the national anthem. United fans expressed their confusion through impolite song. "What on Earth was that?" being the gist of their reply, though their language was considerably more colourful.
A new song about City manager Pep Guardiola got an airing. The song—which suggests his days of hoovering up trophies are over now that he has taken over at the Etihad Stadium—started small but soon spread to almost the whole end.
Guardiola's association with City might have been enough to earn him a disparaging chant, but another motivation for singing songs about the former Barcelona manager is the presence in United's dugout.
Jose Mourinho had his name enthusiastically chanted in the immediate aftermath. Then the Guardiola chant, proving popular, took up again.
Eventually, the United end quietened down a little, but Mkhitaryan's song got another brief outing just before half-time. All told, United fans had hardly stopped singing all game and had rolled out at least 27 different songs and chants.
It took a few minutes of the second half for them to settle back into the event. There was a round of "United!" And around five minutes into the half, Zlatan's song was heard again.
Then came the slightly nonsensical "Na Na Hey Hey Man United," followed by "One of Those Teams."
A short-lived "Calyspo" broke out before a chant of "Rooney! Rooney! Rooney!" in response to the captain winning a corner directly in front of the away support.
The next song that rang out—at top volume from what must have been every United fan in the away end—was Ibrahimovic's, in celebration of his second goal. "Who [on Earth] are Man United?" followed, as it had after the first goal. Then came "The Banks of the Irwell" again. It was a jubilant group of supporters at this point.
Their endorsement of the team's performance, of the style, execution and of the lead, was clear when they began singing Mourinho's name again. Unlike their defiant renditions of "Louis van Gaal's Red Army," during the Dutchman's tenure, this chant carried the full weight of endorsement.
The 2-0 scoreline gave them the confidence to sing a festive classic. Football fans have long adapted "Jingle Bells," this version ending with "oh what fun it is to see United win away!"
The seasonal nature of that song led neatly into another round of the "12 Days of Cantona." Two Cantona songs followed in quick succession—one to the tune of "La Marseillaise" and the other "We'll Drink a Drink to Eric the King."
As controversy brewed on the pitch after a confrontation between Marcos Rojo and Salomon Rondon, United's fans seemed oblivious. The Cantona songs marked the beginning of a trip through the songbook classics. Ruud van Nistelrooy, Jaap Stam and Wes Brown got mentions.
A couple of songs based around taunting Liverpool took over, though they did not seem to quite capture the mood and quickly dissipated.
"Mourinho's red-and-white army" was enthusiastically chanted. Then when West Brom fans sang for Claudio Yacob to the tune of Pilot's "Magic," United's support responded with the Michael Carrick chant, which was one of the originators of the tune's use in a football context.
Having been booed by home fans, Marouane Fellaini got much more positive support from the travelling fans. As he prepared to come on, "If Fellaini scores, we're on the pitch," and "do-do-do, Marouane Fellaini" rang out. It was a loud and sustained chant, a conscious rejection by the away support of the home fans' public criticism.
It is not that he is universally loved among those fans, far from it, but there is a self-identified culture of unconditional support among United's hardcore. This was an expression of that, a clear message.
And that wholehearted support was expressed in the next song. "Forever and ever, we'll follow the boys of Man United, the Busby Babes" is a simple chant but one dripping in subtext about loyalty and long-termism.
Then came an altogether more jovial tune, another airing of "Jingle Bells." By this point, victory felt assured, meaning it was time to serenade the United old boy in the WBA lineup. "There's only one Darren Fletcher," was greeted with respectful applause from West Brom's fans. Then the fast-paced "Darren Fletcher, Football Genius" got a few choruses.
The traditional curtain-closer of "We'll Never Die" began on the 88th minute and was followed by the affectionate "we love United, we do."
There was time for another round of "Jingle Bells" before the 90th minute arrived—it would not be the last.
Ander Herrera's name was enthusiastically chanted as he came off, and Chris Smalling's song briefly greeted his late arrival. Herrera's alternative song, hardly heard at Old Trafford but popular with away fans, also got an outing.
Injury time was played out to the strains of the "United Calypso," and a huge cheer went up at the final whistle.
Then came a genuinely moving moment. As "Jingle Bells" rang out again, United's players went over to the fans. Instead of just applauding, though, they took their shirts off and handed them out, with Paul Pogba handing his to a fan in a wheelchair. It was clearly a bonding moment between the fans and players.
Bleacher Report asked Mourinho about this after the game, and he said he had instructed his players to hand out their jerseys to mark the Christmas season because of how much it could mean to fans. It struck an excellent note, appropriate given that was what those fans had been doing all game.
It is remarkable to think that at least 47 different songs or chants were sung and shouted as the Red Army celebrated their team.
Quotations obtained firsthand.