Manuel Pellegrini described Marko Arnautovic as "a different player" after the Austrian impressed with a brace in a 2-2 draw with Brighton and Hove Albion.
Two goals in two second-half minutes from Dale Stephens and Shane Duffy gave the Seagulls the lead at London Stadium but, after Pellegrini sent on Michail Antonio and Mark Noble, the Hammers levelled matters with two quickfire goals of their own.
Arnautovic's double put him back among the goals for the first time since November 3 as he continued his comeback from a hamstring injury that kept him out for most of December.
And Pellegrini hailed his impact in helping West Ham bounce back from a 2-0 defeat at Burnley.
"He is a different player," Pellegrini said of Arnautovic.
"He is coming back from injury so he is full of energy.
"We know that Brighton score most of their goals from set pieces, especially corners, so to concede two goals from there, knowing that Brighton are good at them, it is very disappointing.
"But fortunately we never gave up. We continued to fight, the two substitutes came into the game and did very well, changed the face [of the game] and I don't remember Brighton having many chances apart from their two set-piece goals.
"Now I hope that we can qualify on Saturday against Birmingham City [in the FA Cup]."
Brighton boss Chris Hughton was the more satisfied of the two managers, and he praised his side's composure after Arnautovic's double.
The Seagulls are 13th in the Premier League table, 10 points clear of the relegation zone after going three matches unbeaten.
He told BBC Sport: "When you are 2-0 up in any game it's hard to take when the opposition get back to level terms. At that stage the momentum was with them, but to gather our composure was pleasing and away from home it was a good performance. I'm delighted with the goals we got.
"We defended really well, particularly in the first half, and there was probably only a handful of times where we didn't defend well and that's where they got their chances.
"Any point here is a good point, but today it's not because we were 2-0 up.
"It could have unravelled, but I thought we knuckled down and showed good composure."
