Jimmy Shan admitted he was not entirely satisfied as Albion won their last home game before the play-off against Rotherham.
The victory over Rotherham relegated the Millers as the visitors put up a spirited performance at The Hawthorns.
The visitors deservedly took the lead after the break when Clark Robertson's effort was adjudged to have crossed the line.
But not for the first time under Shan Albion fought back with two quick fire goals from Jay Rodriguez and Rekeem Harper's first league goal gave Albion the points.
"I think we performed very poorly," Shan said afterwards.
"I wasn't happy with the performance at all. I think you have to take into consideration how blustery the conditions were and them obviously fighting for their lives.
"Their style of play is difficult to contend because they're a forward-thinking team [who] get the ball in and around your back line as frequently as they can.
"I was disappointed with us, trying to get a foothold in the game and some rhythm. I think the team appreciated my frustrations at half time."