The England Under-21 international thanked head coach Steve Clarke for backing him to make an impact against the Barclays Premier League champions.
"It was a brilliant day and a brilliant team performance," said Berahino to the WBA website. "To score at Old Trafford is great too.
"It hasn't really sunk in yet.
"I think it might take a while for me to truly appreciate what has happened. But I'm sure scoring at Manchester United will rank very highly in my career.
"Old Trafford is probably the toughest place to win in football. I think we deserved the win and we created a lot of chances.
"The gaffer told us to go out there and play our football.
"He told us not to be afraid and he made it clear he thought we could win.
"I'd like to thank God, my family, the gaffer and the club for showing so much faith in me."
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