Gareth McAuley headed home in the 80th minute, with what was only the Baggies' second attempt on goal in a lop-sided game, to break the deadlock and substitute Romelu Lukaku doubled the tally 10 minutes later.
The victory marked a dream return to Anfield for Steve Clarke, the former Liverpool assistant coach under Kenny Dalglish, after his side had beaten the Reds 3-0 in the opening game of the season played at home.
"We played well. It's a terrific win for us," the West Brom manager told Sky Sports television on a night that ended a run of six games without a victory with the club's first win of a difficult 2013.
It was their first league double over Liverpool since 1966/67 and also West Brom's first back-to-back win at Anfield - they also won there last season - since 1936/37 and 1937/38.
"Since the turn of the year things haven't gone our way. To come here and play a Liverpool team, probably playing as well as they have all season, I'm absolutely delighted for the players," said Clarke.
The visitors leapfrogged Liverpool to take eighth place on 37 points, behind Swansea City on goal difference. Liverpool have 36.
Goalkeeper Ben Foster was the hero of the evening, saving Gerrard's 76th minute spot-kick after Luis Suarez went down under a challenge from Jonas Olsson.
"When it was given I thought it was harsh. And having spoken to a few people I think harsh is a more than fair description," said Clarke of the referee's decision.
"You get the luck but it's not luck because Ben Foster is a great goalkeeper... the penalty save was crucial and I think it gave us a little bit of positive momentum to go on and do what we did in the last 15 minutes."
Foster also denied Gerrard in the 50th, when he smothered a close-range effort by the captain, and 20 minutes later when he kept the ball out of the net with a superb one-handed reflex save.
The visitors had never threatened in a muted first half while Liverpool had Jonjo Shelvey clearly offside after he had the ball in the net in the eighth minute and Luis Suarez refused a penalty claim.
"I thought we were always on the front foot, looking to get the goal," said Liverpool manager Brendan Rodgers. "Their keeper's made some outstanding saves and obviously we then conceded at the other end... bitterly disappointing."
Liverpool missed the pace of the injured Daniel Sturridge up front while West Brom managed well enough without Peter Odemwingie.
The West Brom striker was an isolated figure, seen texting in the stands after failing to make the bench following his much-derided attempt to join Queens Park Rangers in the January transfer window.
