Two goals from Marlon Harewood helped West Ham notch a club record-equalling seventh straight win and add to Birmingham's relegation worries.
Harewood netted in either half for West Ham
His first came when he was quickest to react to a lucky bounce off defender Kenny Cunningham.
The second arrived after the hour mark when he followed up his own saved penalty after a Martin Latka handball.
Dean Ashton soon added a third to wrap up an easy win against a Blues side who did not seriously test Shaka Hislop.
The victory sees West Ham move up to sixth in the Premiership, but leaves Steve Bruce's Birmingham side six points adrift of safety and deep in trouble.
After a sluggish opening, West Ham went ahead when Harewood made the most of sloppy defending by the visitors to fire powerfully past Maik Taylor.
Hayden Mullins soon had a chance to double the lead after a poor clearance by goalkeeper Taylor, but Alex Bruce took the ball off his toes as he lined up the shot.
Just as they seemed to be on the verge of taking charge of the game, West Ham seemed to go off the boil and allow the visitors back into the match.
Most of Birmingham's threat came on the left through Jiri Jarosik, but he could not find a way past Anton Ferdinand and Danny Gabbidon and was restricted to unconvincing long-range efforts.
Early in the second half the game seemed to be creeping towards something dramatic happening, and it duly did when West Ham scored twice in three minutes.
First, Harewood followed up to net after Taylor blocked his penalty following Latka's indiscretion.
And shortly afterwards record signing Ashton made it two goals in as many home starts when he stooped to head in Yossi Benayoun's flick-on at the far post.
The double strike killed off the match as a competitive spectacle, although Jermaine Pennant flashed in a couple of long-range free-kicks to give Birmingham some hope.
But they were reduced to off-target speculative efforts as Hislop was never seriously tested, and the final outcome was never in much doubt.
West Ham manager Alan Pardew on rising to sixth in the table:
"A number of sides have got to this position and fallen away, but we can't afford to do that.
"These players are hungry and young so we've got to keep pushing ourselves.
"This team has good spirit and if I can keep it together for the next few years we can challenge the big boys. We're making small steps towards that."
Birmingham boss Steve Bruce on their next three games against fellow struggling sides:
"The one thing we must do is show more resilience than we did here because we're in a relegation scrap.
"We've got to scrape and fight and show a bit more, especially going forward, to try and get the results we need.
"It'll be difficult but we're ready for the challenge ahead and I'm sure we can try and do it."
West Ham: Hislop, Scaloni, Ferdinand, Gabbidon, Konchesky, Benayoun, Mullins (Dailly 46), Reo-Coker, Etherington (Katan 77), Ashton (Zamora 77), Harewood.
Subs Not Used: Bywater, Sheringham.
Goals: Harewood 11, 63, Ashton 65.
Birmingham: Maik Taylor, Melchiot, Cunningham, Latka (Clapham 71), Gray, Pennant, Bruce, Clemence, Jarosik (Painter 71), Sutton, Forssell (Campbell 67).
Subs Not Used: Vaesen, Birley.
Booked: Bruce, Latka
Ref: D Gallagher (Oxfordshire)