Alan Pardew says Albion's injury hit side looked tired during their 3-2 defeat at home to Southampton.
The Baggies had a dream start when Ahmed Hegazi nodded home Chris Brunt's corner inside five minutes.
But Albion were behind at the break after two quick fire goals from Mario Lemina and Jack Stephens.
It got worst for Albion when James Ward-Prowse fired in a free kick from 20 yards.
Salomon Rondon's header pulled one back but Albion were unable to find an equaliser and now find themselves four points adrift of Premier League safety.
“I thought our options were limited in terms of resting certain players today," said Pardew after Jonny Evans, Kieran Gibbs, Ali Gabr, James Morrison, Jake Livermore, Grzegorz Krychowiak, Nacer Chadli and Hal Robson-Kanu all out injured or not fit.
“I think we covered more distance at Manchester City on Wednesday night than we have in any other game this season.
“And I think that showed today. Southampton looked a yard quicker than us.
“The 20 minutes before half-time knocked us.
“We couldn’t get a grip of the game and they were dominating.
“It was unfortunate for us that they scored twice in that period with two quick goals.
“We huffed and puffed in the second period and pushed the game, but we didn’t really threaten enough.
“When you’re up against a team that are a little bit fresher they can slow the clock down and manage the game which was frustrating for us.”