And indeed, if they wanted to reclaim their spot at the top of the leader board, they would have to. Not only was a victory necessary, they would have to at least match City's scoreline.
On Wayne Rooney's hat-trick, they did so. And on Javier "Chicharito" Hernandez's brace, they surpassed it.
So, here are five thoughts from a thrilling night at the Reebock.
Maybe it really is the hair transplant.
At this time last season, Wayne Rooney was a shell of himself. Cursed with a leaden first touch, a sour expression, and a seething, raging turmoil for all to see, people were asking the inevitable question of whether the boy wonder was done for.
Well, Rooney proved his doubters wrong with one of the best starts to a season a striker can ask for, bagging eight goals in four games. In fact, with his hat trick against Bolton, he has accomplished what only Les Ferdinand, Ian Wright and Didier Drogba have been able to in the Premiership era: score hat tricks in consecutive games.
But it's not just the goals that caught the eye in Rooney's performance today.
The lad has always had bounds of energy and strength, and throughout his career he's used both to carve defenses to pieces. But he's also been wild, temperamental and a danger to be sent off at any given moment. For every sublime goal or pass to set up a goal, he would hack down an opposing player in his own half or stomp on an opponent's leg.
But in a young season where United fields a young team on which Rooney, at 25, is an elder statesman, the former boy wonder has grown up and become a leader on the field.
On this day against a tricky opponent, he's harnessed his energy and shown the qualities that have led pundits to predict that he is next in line for captaincy of club and country.
Aside from scoring his hat trick, he also helped set up Chicharito's early goal. In that space of time between Tom Cleverley's injury and Michael Carrick's appearance, Rooney dropped back into midfield and helped Anderson carry the load. In fact, he looked like an excellent midfielder in his own right, and could conceivably slide in there should Sir Alex Ferguson decide he wants to start Chicharito and Danny Welbeck together someday.
Selfless tracking back has always been a part of his game, something that differentiates him from the likes of Cristiano Ronaldo. He showed that again today, even clearing a ball off his own goal line.
Calm and composed throughout the match, he exemplified the hard work and creative flair that has characterized Manchester United in the early goings. If he keeps it up, he may just challenge Lionel Messi for the title of "Best in the World."
The young man they call "Chicharito" turned many heads last season when he scored 20 goals in 45 appearances in all competitions.
Showing a natural predatory instinct reminiscent of former United great Ruud van Nistelrooy and current teammate Michael Owen, Chicharito provided such an impact that he displaced Dimitar Berbatov in the starting line-up towards the end of the season. It looked like, in Chicharito and Wayne Rooney, United had their starting strikeforce set for years to come.
But then Chicharito suffered a concussion in training during the offseason, and he was sidelined for weeks. In the interim, young Danny Welbeck came back from loan and slotted into the starting eleven.
And Welbeck was a revelation, showing strength and predatory instincts of his own, and building up a good understanding with Rooney in the process. At that point, many pundits began to doubt whether Chicharito could snatch his spot back.
The young Mexican was given a chance against Bolton due to Welbeck picking up an injury of his own.
And he made the most of it.
His two goals showed the same lethal predatory instincts that had initially made fans sit up and take notice. His constant movement off the ball and general good understanding with Rooney, Nani, and Ashley Young was a thing of beauty.
United seems to be a more lethal side when Chicharito plays, which I think he proved today.
During the galactico era of Zinedine Zidane, Ronaldo, Luis Figo, and Roberto Carlos, Real Madrid bagged scores of trophies on the strength of an overpowered first team and an extremely weak reserve squad.
Such a philosophy would not work in today's footballing world, and, thankfully, Manchester United has built a team with true depth. The sort of talent languishing on the bench would make most other team's starting eleven, and at the start of the season it almost looked like a luxury.
Well, luxury has become a necessity, especially after the events of Saturday's game.
Already without the services of captain Nemanja Vidic, striker Danny Welbeck, midfielder Darron Gibson, and (former) first choice right back Rafael, United saw another soldier fall in action against Bolton.
Tom Cleverley, the youngster who quickly showed that Wesley Sneijder was not needed, was the first to fall. It was a (typical) Kevin Davies horror tackle that took the youngster out of the game in the eighth minute. He would not return, and it would later be revealed that he suffered a broken foot that may keep him out for quite some time.
Later, Jonny Evans picked up a knock of his own, although it didn't look too serious. Still, it necessitated a substitution.
And it's these two substitutions that showed United's depth, something they'll have to call upon in the months to come.
Michael Carrick came on in Cleverley's place, and while he is no longer the player he once was, he still put in an admirable performance in the center of the park. Still showing a good shot and good vision, he played off of Anderson's driving energy quite well, and it was his deflected shot that provided Chicharito with his second goal.
Chris Smalling, rested at the start, came on for Evans. For most, that in itself is an upgrade, and the England international didn't miss a step.
Sir Alex Ferguson rarely calls upon the same starting 11 week in and week out. As the season rolls along, as injuries and suspensions pile up, United's squad depth will become more important than ever.
If there was any game that De Gea would have been dropped for, it was this one.
Bolton is an intensely physical team, known to cause havoc in penalty boxes and capable of bullying less imposing keepers. In other words, the kind of team who could feast on De Gea's physical weaknesses.
Indeed, there were rumblings that Sir Alex Ferguson would drop the Spaniard in favor of the much more imposing Anders Lindegaard.
But Sir Alex stood by his keeper, showing his faith in the youngster and thereby proving that De Gea is most certainly looked at as Edwin van der Sar's long term successor. As a result, De Gea's confidence in himself must be pretty good at the moment.
And De Gea obliged his manager by keeping a clean sheet and even managing to pull off a good save down and to the left, the kind of shot that would have given him trouble were his confidence shot... something that may have happened had he been dropped.
For years, John O'Shea filled a special role in the Manchester United squad.
Blessed with enviable versatility, O'Shea was deployed as a left and right back, as a center back, a defensive mid-fielder, a striker, and even an emergency goal-keeper. While he was never really the best at any of those roles, he filled them adequately, exemplifying the descriptor of "Jack of All Trades, Master of None."
When he was sold during the summer, many fans lamented his loss, as we weren't sure where such versatility would be found again.
Until we looked at the right side of our defense.
In Phil Jones and Chris Smalling, younger versions of Nemanja Vidic and Rio Ferdinand, it is quite possible that we could be seeing England's first choice center-back partnership right here in United.
Both are strong defenders with good footballing minds, blessed with good speed and tough tackling skills. They are perfect fits in United's system, and many believe that they will supplant both Vidic and Ferdinand in the near future.
And yet, both have show that they are capable of playing out wide at right back, with Chris Smalling even establishing himself as England's first choice.
With Smalling rested against Bolton, Jones took his turn at right back and showed that he might be just as good or even better. Playing in the center in previous appearances, Jones had shown himself to be quite comfortable with the ball at his feet.
But against Bolton, he showed a willingness to bomb up the right lane and supply some surprisingly accurate and well-weighted crosses. In fact, he was directly involved in Wayne Rooney's first two goals.
For the first one, he provided a pin-point cross for Rooney to tap in. For the second, he showed off decent dribbling skills to weave into the Bolton area and unleashed a shot that goalkeeper Jussi Jaaskelainen could only divert into the onrushing Rooney's pass.
Throughout the game, Jones played an almost perfect right-back, and it will raise arguments about whether Smalling or Jones will be preferred.
But playing for Blackburn, Jones also showed a side that United fans have yet to see. He is also quite a capable holding mid-fielder, due to his good positioning sense, defensive abilities, and passing vision. If need be, I think we'll see Jones in the midfield before the year is out.
Now if only he can play goalkeeper...
And there you have it. A five-star performance against a scrappy Bolton side has taken United back to the top of the table.
With United and City matching each other performance for performance, it's looking more and more likely that the premiership is becoming a two-horse race.
October 23, when the pair faces off, cannot come fast enough.