They are not used to that
Many will have expected United like they have so many times in the past under Mourinho's watch to park the bus against the big sides, and with a lot made of his recent record against the 'big sides' it did look like the coach was looking to eradicate that with his tactical tinkering.
The two up-top method certainly paid off midweek as they eventually swept past Watford as 4-2 victors, and it proved effective early on at the Emirates Stadium as the unchanged side produced two early goals through Antonio Valencia and Jesse Lingard.
United were continuously bombarded by The Gunners which saw them rewarded with a goal through Alexandre Lacazette, but a swift counter-attack and finish from Lingard in the second period secured all three points.
The effectiveness of the striking partnership of Anthony Martial and Romelu Lukaku with Lingard just behind will fill fans with hope with Sunday's Manchester derby on the horizon, and post-match Smalling stated that this change was crucial in the defeat of Arsène Wenger's men.
"I think we were carrying on from Watford," Smalling explained to MUTV. "And the fact that, when we play, obviously in this system, we can play with two strikers."
"Quite often, they [Arsenal] are only used to playing against one," the defender proclaimed. "We put two up front and put them under more pressure and they are not used to that."
"I think that was one to enjoy," he stated. "For fans watching the game and for us as players."
"It was end to end, but for us to get those two early goals," Smalling added. "I think, meant Arsenal had to come at us and that’s what made it a very entertaining game."
Despite the scoreline it certainly wasn't an easy ride for The Red Devils, with the home side peppering their goal with excellent opportunities straining their defence which was stretched further with the sending off of key midfielder Paul Pogba.
Many players stood out in North London but one that shone brightest was David De Gea, who put in one of the best goalkeeping performances of recent memory to keep Arsenal's goalscoring down to just the one.
The Spaniard managed to make 14 saves throughout the 90 minutes which was the joint highest total in a Premier League game alongside Tim Krul and Vito Mannone since Opta records began, and post-match admitted that he "sometimes" felt unbeatable inbetween the sticks.
“Sometimes," the goalkeeper said when asked if he felt unbeatable. "You just start a game with a really good save, with a good feeling."
"You feel that [unbeatable] but we started the game really well," the Spaniard proclaimed. "We scored two important goals."
"And it’s true that we lost a bit of a control of the game after," De Gea concluded. "But it was a good performance.”