The Blues raced into a two goal lead within the first 18 minutes through Michael Essien and Salomon Kalou, both strikes down of the Hammers own making.
Essien added his second late-on but there was still time for the home side to net a consolation from Scott Parker, which did little to ease the pressure on boss Avram Grant.
Tim Cahill and Mikel Arteta then scored in added time to send the home fans into raptures.
Blackpool continue to defy the pundits who had them favourites for an immediate return to the Championship.
The Seasiders took all three points in the clash of the promoted sides at St James' Park with a Charlie Adam penalty just before the break and then a late effort from DJ Campbell.
This 2-0 win sends Ian Holloway's men soaring into the top four of the Premiership.
City dominated with Adam Johnson and Carlos Tevez a constant thorn in Rovers side.
Yet it was the visitor's who took the lead through Nikola Kalinic in the first half after an horrendous mix up in the City defence presented the striker with an open goal.
Patrick Vieira levelled soon after the break but for all their pressure Blackburn's defence held firm for a battling point.
Fulham's 2-1 home win over Wolves came at a price as Bobby Zamora was stretchered off with a broken ankle.
Wolves took an early lead courtesy of Jelle Van Damme before Zamora left the field after half-an-hour.
But Moussa Dembele bagged a second half brace whilst the visitor's Christophe Berra saw red for two bookable offences.
Arsenal had a routine 4-1 victory over 10-man Bolton at Emirates Stadium.
Laurent Koscielny opened the scoring for the Gunners before his mistake then gifted Wanderers an equaliser Johan Elmander shortly before half-time.
Marouane Chamakh restored the Gunners lead before Gary Cahill was harshly dismissed by referee Stuart Atwell.
Alex Song and Carlos Vela then took advantage of the one man advantage with strikes in the closing stages.
Tottenham took the lead but had to settle for a point in a 1-1 draw on their visit to West Bromwich Albion.
Modric then left the field injured and headed down the tunnel on crutches.
But the home side restored parity before the break with Chris Brunt nodding home from close range.
Sunderland's £13m striker opened his account in the 1-1 draw at Wigan.
The Latics earned a point with three minutes remaining, Antolin Alcaraz depriving the Black Cats of all three points.