Alvarez came on just before the hour mark to form a strike partnership with fellow forward, Erling Haaland.
And the Argentina World Cup winner’s ‘dynamism’ caught Onuoha’s eye in the important victory at Selhurst Park.
He said: “I have to give credit to Alvarez. When he came on, I thought he did really, really well.
“He had a chance to score what would have been an incredible goal with the little turn and shot.
“I thought his dynamism going forward, his selfless running and his eye for goal caused Palace some significant problems.”
WATCH: Crystal Palace 0-1 City: Extended highlights
Onuoha believes it was a ‘big statement’ by Pep Guardiola to bring on Alvarez so early in proceedings, away from home.
But it was one, stresses Onuoha, that turned out to be a masterstoke as City earned all three points to keep the pressure up on top-of-the-table Arsenal.
He added: “I think he was brought on in the 58th minute so City going for it, away from home, that early, that’s a big statement in itself and thankfully we were rewarded for it today.
“City were controlling the midfield. In my opinion, from my perspective, for the vast majority of that 60 minutes Palace were very much on the back foot and City didn’t need an extra body in midfield controlling the game.
“So to put two players up there – but to still have a bit of width within it – I think it meant defensively Palace were that bit more reluctant to make that step forward.
“For Pep, it was a clear statement with two forwards and, for as much as we can move the ball side to side, here are the players who are going to be more incisive and here’s the player who will stretch the game in behind.”
