Head coach Pepe Mel felt Pablo Zabaleta's early goal did for West Brom in a 3-1 Premier League defeat to Manchester City on Monday.
Mel saw his West Brom side go two goals down at the Etihad Stadium after the opening 10 minutes thanks to Zabaleta's acrobatic header and Sergio Aguero's long-range effort.
Graham Dorrans pulled a goal back after 16 minutes before Mel's relegation-threatened team began to frustrate City and look as though they could spring a surprise - as Sunderland did with their draw on Wednesday.
While Martin Demichelis prodded home a third after 36 minutes, Mel was heartened by West Brom's efforts for the final 70 minutes.
"Conceding the goal in the third minute meant we had to change our plans," he told Sky Sports.
"The players really did try in the remaining 70 minutes.
"We came across a big strong rival who are fighting for the Premier League."
It leaves West Brom two places and three points above the drop zone going into their final games against West Ham, Arsenal, Sunderland and Stoke City.
Mel feels Saturday's clash with West Ham is crucial to their survival hopes as they look to take advantage of the game in hand on the three teams immediately beneath them.
"In the next game, it truly is like a cup final," he added.
"The whole year is based on this game against West Ham."