A solitary goal from Wolverhampton-born Sam Morsy was enough to earn the Latics all three points at The Hawthorns - with the visitors worthy of their win.
Slaven Bilic's side entered the game following five excellent performance against Millwall, Reading, Nottingham Forest Bristol City and Preston North End.
But they struggled to find any rhythm in what was there seventh game of the month.
And Bilic conceded post-match his team did look short on energy.
"We knew it was going to be a hard game," the head coach said.
"We told the players, they knew. Simply we weren’t good enough.
"We looked tired, without spark and without the fluidness we’ve had in a lot of games this season.
"We were second best. We didn’t manage the ball well, we played too hectic, too direct and without pushing up to get those second balls.
"We tried to change it, in the second half with new players, but it wasn’t to be.
"You can’t say we were unlucky, no. A draw might’ve been a fair result, but if you don’t win these games you must make sure you don’t lose them. "Ultimately we conceded a goal from a set-piece and that was pretty much that."
Bilic says there was no indication before the match his team would be so flat.
"We spoke with the sports science guys - we looked well, and looked well mentally of course.
"We'd won five of the last six. We had belief.
"It didn’t look like we were tired or whatever on data, or talking to the players yesterday - we looked okay.
"But we didn’t have that energy, team energy that we had recently and in this league, you have to have it, otherwise your chances drop big time."
As well as losing the game, Albion also saw Ahmed Hegazi come off before half-time with a hamstring injury.
"It’s disappointing for him," Bilic added.
"He’s done really well, he worked so hard to get back in the team. Since he came back he was outstanding for us.
"That energy from the back. Unfortunately, he did it.
"It’s too early to say how bad it is. We have to wait for the scan, but it’s definitely not a knock, it’s not cramp. It’s not a couple of days.
"Hopefully, it’s not a big one. Hopefully, he’ll be back soon, but we have to wait for the scan."