Bruno Fernandes conceded Manchester United can do "a lot better" after his penalty sealed a first home league win of the season.
Ole Gunnar Solskjaer's side have failed to win in their first four outings at Old Trafford, losing three and drawing one.
But they finally secured the three points courtesy of a Fernandes penalty, albeit at the second time of asking after a retake was ordered following Sam Johnstone's save.
The Portuguese star was angry however an needing a second bite of the cherry.
"It was really important to us to win this game because we need the points," he said.
"It was a tough game. We can do a lot better. We created a lot but we have the quality to do better."
Before adding when asked about missing his first penalty: "It's not good. You need to do it on the first one. I'm not happy. I scored the second one but I didn't the first one."
Fernandes was involved in several of the games key moments as it looked as if he'd given away a penalty with the game goalless.
He was adjudged by referee David Coote to have fouled West Brom's Sam Gallagher.
But the official then changed his mind when asked to review his decision on the pitchside monitor.
"I felt I touched the ball and it was the second contact," said Fernandes.
But former Red Devil Rio Ferdinand blasted Coote's decision to overturn his original call.
"It's a disgraceful decision," he said.
"He got it right first time. It's a nailed-on penalty. How can he go against his own decision on that?"
Baggies boss Slaven Bilic also hit out and claimed his side's inferior status contributed to the decision.
"I'm very disappointed with the decision," he said.
"I felt like 'small West Brom'. All those crucial decisions went against us. I've watched it a few times and it's a clear penalty. I don't understand why he overturned it."
