Christopher Samba had opened his goalscoring account for ten-man Blackburn early in the second half, but a dubious Carlos Tevez penalty and substitute Bobby Zamora's close-range strike, which appeared to bounce back off Tevez on the Rovers goal-line, handed the Hammers an unlikely, but crucial, three points.
On a miserable evening in Lancashire, both sides took time to find their feet on the worn and waterlogged pitch.
Tevez and Morten Gamst Pedersen both fired comfortably into the arms of the respective goalkeepers inside the opening eight minutes, before West Ham keeper Robert Green was thankful to hear the referee's whistle after dropping Brett Emerton's cross under supposedly too much pressure from David Dunn, leaving Matt Derbyshire with the simple task of rolling the ball home.
And Green was breathing a sigh of relief just three minutes later. David Bentley picked out Benni McCarthy with a fine through ball, the South African had to hurdle the challenge of the onrushing keeper and when the Rovers striker looked to centre from the right, the retreating Green connected with the ball and almost fired it into his own net.
On 17 minutes, Derbyshire almost connected with Pedersen's first-time cross after some trademark stuff from Tugay and ten minutes later, the visitors had their best chance of the half, when Tevez's flick found Marlon Harewood inside the box, but the Hammers striker volleyed wide of the mark with a clear sight of goal.
Pedersen struck a swerving volley well wide on 35 minutes, before the Norwegian ought to have handed Rovers the lead five minutes later, but after finding himself clean through on goal, his dinked effort over Green bounced agonisingly wide of the post.
But the in-form winger made amends just two minutes after the break when his inswinging corner from the right was powerfully headed home by Samba from close range.
The Hammers responded well and almost equalised on 66 minutes when Matthew Etherington found himself clean through after a quick break, but his chip over the onrushing Brad Friedel was hooked clear by Stephen Warnock close to his line.
But moments later and the visitors were level. Emerton was deemed to have brought down Tevez inside the box, although replays showed that there was minimal contact if any, and the Argentinian got up to stroke home from the spot.
And just three minutes later, West Ham were awarded their second contested goal of the game. After a scramble in the box, Zamora's goal-bound effort struck Tevez on the line and bizarrely the near-side linesman signalled for a goal.
Rovers threw everyone and everything forward in the closing stages, but only achieved a second red card in as many games, when Bentley picked up his second booking for handball in time added on.