United failed to score four goals in a first half under Ten Hag, as they did against Leicester.
Yet Van Nistelrooy was honest enough to admit they had created more and better chances at Crystal Palace, Fenerbahce and West Ham this season and won none of those games. Sometimes, he admitted, you need “a little bit of luck”.
Leicester boss Steve Cooper remarked that he was surprised at the atmosphere inside Old Trafford: “It wasn’t what we were expecting. It wasn’t intimidating at all. It was good to play in.”
That is a bit harsh. United’s fans got behind their team and they provided a performance.
Van Nistelrooy was clearly focused.
In the first few minutes he was so embroiled in the game he was halfway across Cooper’s technical area before he was guided back to his own by fourth official Michael Salisbury.
His celebration of Casemiro’s opener was that of a man who was living a new reality having enjoyed so many memorable Old Trafford days 20 years earlier.
He made a point of having a word with both Marcus Rashford and Alejandro Garnacho when he replaced them during the second half. He will know more than most how valuable confidence is for an attacking player.
His demeanour was one of professional pride and a determination to do his job properly and to the best of his ability.
We do not know what Ten Hag thought, or what Amorim made of the victory, or a quarter-final trip to Tottenham, which will almost certainly be his to fulfil in the middle of next month.
Van Nistelrooy cannot know how many more days there will be. But he does know, on this one, he did well – and he enjoyed it.