Goals from Steve Claridge and Shaun Derry gave Portsmouth hope in their battle against the drop from Division One as Baggies captain Matt Carbon was sent off in a full-blooded affair at Fratton Park.
Portsmouth were always in charge once Claridge had given them the lead from the penalty spot after 26 minutes after he was brought down by a clumsy challenge from Baggies goalkeeper Brian Jensen.
Claridge made no mistake from the penalty spot, sending Jensen the wrong way to claim his 12th goal in his last 15 matches for Portsmouth and send Tony Pulis' side on the way to victory.
West Brom boss Gary Megson was banished from the dug-out after complaining to referee Graham Poll about the spot kick award on a disastrous night for the club from the Hawthorns whose own First Division future is in the balance.
Referee Poll kept his cards in his pocket despite some hefty challenges in the first half but he flourished six in the second half and dismissed captain Carbon for a second bookable offence in the 71st minute.
Carbon had already been cautioned for a needless challenge on Lee Bradbury after 60 minutes when he once again bundled over the Portsmouth striker, clipping his heels from behind as he ran through on goal. Referee Poll had no alternative but to produce a second yellow.
To compound West Brom's misery, Portsmouth's new signing Derry marked his home debut with an 85th-minute goal to put the game beyond the visitors.
Derry, on his home debut following a £600,000 move from Sheffield United last week, ran 25 yards before beating goalkeeper Jensen with a right-foot shot which went in off the post.
West Brom struggled to get back into the game and created few chances with a glancing header from Carbon in the first half, which hit Aaron Flahavan's right-hand upright, their only effort of note.
Derry also hit the woodwork for Portsmouth as did veteran Claridge and Lee Bradbury blazed over the bar from eight yards when he should have scored.
West Brom's only other decent effort came in the 53rd minute when Jason Van Blerk shot over from 20 yards out with a right footed curler which appeared to have caught Flahavan off his line.