It may have been his two goals that propelled Cristiano Ronaldo to today's back-pages, but something else caught the eye later on.
As United cleared an Arsenal corner in the 88th minute, they sensed a chance to counterattack, already 3-2 up at the time.
Jadon Sancho dribbled almost the full length of the pitch before squaring for Bruno Fernandes - one of the goalscorers.
The Portugal international struck a weak shot against Gabriel, meaning United didn't extend their lead.
But Unseen by Sancho and by most of the Arsenal defence was Ronaldo, who had busted a gut to belt it down the left flank, offering support.
As soon the ball was played not to him but to Fernandes, he leant down and took a breather, visibly struggling with hamstring pain. He came off just seconds later with a hamstring injury.
It was a moment that just exemplified the United legend's elite mentality.
There is little chance of Ronaldo still being the top scorer in men's international football history - along him holding most of his other ridiculous records - did he not possess such an elite, professional mentality.
The biggest names at Manchester United were saying before his arrival that they can't wait to see how the Portugal talisman trains. That says it all.
While more players have scored higher numbers of goals - many more goals, in fact - Ronaldo's double against Arsenal were his 800th and 801st top-level goals.
He is the first player in the history of the sport to score that number of goals at the elite level. The second-half double took his personally career tally against the Gunners up to eight goals.
United supporters now have a slightly uncomfortable wait on their hands as they prepare to find out how badly injured their No 7 is.
However, it did seem like the sort of muscle twinge older players get from time to time, rather than a pulled hamstring which might be more serious.
Ronaldo now has six Premier League goals this season. Only Mohamed Salah, Jamie Vardy, Diogo Jota and Sadio Mané have more.
Words by Dom Smith
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