Zigic bags Birmingham vital victory
The giant Serbian striker headed home from close range after 65 minutes to earn three precious points in a relegation scrap involving the entire bottom half of the table.
Defeat meant West Ham returned to the foot of the table with 24 points from 26 games, below Wolverhampton Wanderers, who beat leaders Manchester United on Saturday, on goal difference.
Wigan Athletic complete the bottom three with 26 points while West Bromwich Albion, who parted company with manager Roberto Di Matteo on Sunday, are just above the drop zone thanks to a marginally better goal difference.
Birmingham have 27 points but have at least one game in hand of all the teams struggling to avoid the drop.