"Three days ago we embarrassed our football club so there is an extra smile on my face," said Glenn Roeder after Hammers climbed to just within one point of safety.
"It's a massive win and we hope it's the turning point in our season, this has made us believe we can stay up but there is still a lot of hard work to do."
Roeder, who described his sides performance in Sunday's 6-0 hammering at Old Trafford as totally unacceptable, made five changes from the team that folded so badly against Manchester United.
And the injection of Paolo Di Canio, Les Ferdinand plus defenders Nigel Winterburn, Tomas Repka and Glen Johnson certainly added some early bite and fight.
On the half hour, David James nervousness almost cost the Eastenders dear when he was lobbed by Andy Cole, only for Lee Bowyer to head off the line.
But seven minutes later, West Ham were not so fortunate when David Thompson's by-line free-kick dropped to the unmarked Dwight Yorke in the six-yard box and the Rovers striker prodded home at the second attempt.
The Hammers endured a frustrating start to the second period, too, but on 57 minutes Joe Cole's electric burst saw Di Canio tripped by Andy Todd and the Italian dusted himself down before sending his spot-kick right down the middle as he celebrated his influential return.
In reply, Yorke had valid claims for a penalty while Cole's 35-yarder flew inches wide.
At the other end, Friedel denied both Bowyer and Di Canio, but just when it looked like ending all square, that man Defoe chested down Cole's crossfield pass and drilled a low, angled 12-yarder inside the Blackburn keeper's near post to net his ninth of the season and finally give the patient Upton Park faithful that long-overdue win.