Injury and suspension made it the area of the pitch that was supposed to be Manchester United's weakness but it turned out to be their strength.
Just over a year ago now, Scott McTominay became the pawn in Jose Mourinho's public tussle with Paul Pogba. United's last European knockout game away from home - in Seville last February - was the crucible in which the young midfielder had to prove his credentials.
McTominay acquitted himself well enough that night, but the question of whether he was promoted as part of a point-scoring exercise rather than on any particular merit have surrounded him since.
For Fred, the third-most expensive signing in United's history at £52m, the scrutiny has been only more intense. Until last Wednesday, he had made just 15 appearances for his new club and only three under Solskjaer.
When he was overlooked as an option off the bench as muscle injuries ravaged his team-mates during the recent draw with Liverpool, it appeared to say everything about his standing at Old Trafford.
He was drafted into the starting line-up at Crystal Palace three days later because there simply was nobody else of a senior standing left to play in his position. The same was true last night at the Parc des Princes.
That both McTominay and Fred should start this critical second leg against Paris Saint-Germain as a midfield two against Marquinhos and Marco Verratti did not inspire confidence, especially on a night where United's first task was to not fall further behind.
And to suggest that they dominated and controlled the play in the middle of the park over the course of the 90 minutes that followed would be inaccurate. No team whose share of possession dropped as low as 11.9 per cent could claim that.
But Solskjaer was not asking for them to dictate the tempo, he was asking them to disrupt it. Their task was to get among PSG, to harry and harrass them, and to spread the nervous energy that could bring about a collapse.
In this regard, they were successful. Nobody made more tackles on the night than McTominay's five. Fred's three was the next most of any United player. Their attempts to seize possession did not always bear fruit but they exerted pressure relentlessly.
Even once PSG settled down and stopped making the errors which led to Romelu Lukaku's two first-half goals, during a largely sedate second half when a goal would have killed United off, they were stifled. There were few, if any, clear chances after the break.
Though inspired by their mutual Scottish blood, the comparisons between McTominay and Darren Fletcher are growing. A player who can be trusted to do the less glamorous work well is necessary to any side.
Fred's most significant contribution, meanwhile, may have come right at the end. As Marcus Rashford stood over what-would-be the decisive penalty kick for several minutes, his team-mate snarled and shoved every PSG player attempting to intimidate him.
Their manager was unequivocal in his praise for them and especially the Brazilian, for who Solskjaer said last night was a "breakthrough". "They did a fantastic job, screening in front of their high midfielders and putting pressure on Verratti and Marquinhos. Excellent."
Solskjaer had every reason to be grateful. He had demanded more of McTominay and Fred than they had ever previously shown in a United shirt but both delivered, playing understated yet integral parts in one of the club's greatest European wins.
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