It's difficult to know what exactly makes a big game big.
Television companies keen to sell their wares advertise every game they broadcast in a manner that suggests the fate of the free world rests on its outcome. Premier League managers, observing the niceties, do their bit too.
“It's a big game,” they say in unison before each game, regardless of the opponent or venue.
Like most managers, Sir Alex Ferguson would participate in the phony war. But when his side were in full flow, there was sometimes a sense that teams would settle for a narrow defeat and a day off instead of making the trip to Old Trafford and and running the risk of getting thumped.
Mick McCarthy once rested all 10 outfield players at Old Trafford when he was manager of Wolves. Neil Warnock did something similar when he was in charge of Sheffield United, although not quite on the same scale.
The thinking was that their team was likely to lose whether they were at full strength or not and it would be better if the first-team players saved themselves for more winnable games in the future.
For the record, McCarthy's Wolves beat Burnley 2-0 four days after his reserves lost to United.
Like Ferguson, David Moyes has taken part in the familiar pre-match dance. But when he's talked of big games in his new role as United manager, he's sounded like he meant it.
Because as he tries to smooth the transition from legend to learner, every game is a big game.
United were used to winning under Sir Alex Ferguson. It became such a habit that one defeat was a crisis. Two in a row was treated like the end of the empire. That's the level of expectation Moyes is facing at Old Trafford.
But it's not just the expectations at his own club he's battling against.
Upon his arrival at United, he's found opposing teams that are hoping to cash in on the summer upheaval, sensing an opportunity for a rare win at Old Trafford.
Nani said as much this week in an interview with Sky Sports, observing, “It looks like teams are more confident when they come here to play against us.”
West Brom, Southampton and Stoke didn't just arrive at Old Trafford with their first-choice XIs, but also with a belief that they could win. West Brom, in particular, showed what a dangerous combination that can be.
Three wins from six Premier League games at Old Trafford this season—and a scare against Stoke—has fuelled a feeling that anything can happen in United's home games.
The atmosphere inside the ground during wins over Liverpool and Arsenal told its own story. They are two of United's traditional rivals, but the noise created by fans was similar to what you'd expect for a Champions League semi-final.
It was almost as if home wins over Liverpool and Arsenal couldn't be taken for granted anymore and should be celebrated as such.
It doesn't take much for the aura of invincibility to slip, but it takes a while to get it back.
United started to rebuild their fearsome reputation when Arsenal visited a week ago. Moyes will hope the repair job continues when Everton, Newcastle and West Ham arrive next month. Then, slowly, some big games might not appear so big after all.