Blundering Ben Foster may have saved Avram Grant's job as 10-man West Ham survived a moment of madness from Victor Obinna to beat Birmingham in the first leg of their Carling Cup semi-final.

England goalkeeper Foster allowed a powder-puff shot from substitute Carlton Cole to squirm through his legs after Obinna looked to have cost the Hammers dear by crazily kicking Sebastian Larsson in the groin.

Rightly sent off, Obinna had been central to a sterling first half from the home side, which saw Mark Noble deservedly put them ahead, arguably with the help of another Foster error.

Former West Ham trainee Liam Ridgewell levelled after the break and the visitors looked set to go on and win before Foster's howler.

The prospect of West Ham's first League Cup final for 30 years had failed to quell the speculation over Grant's future, with some reports suggesting even a win tonight would not be enough to spare him the axe.

Despite Birmingham being only two points clear of the Hammers, manager Alex McLeish was under no such pressure as he looked to lead them to their first final since 2001.

But his team did not start like that as West Ham bossed the first half virtually from start to finish.

Captain Matthew Upson set the tone from the unfamiliar position of left-back, an inspired selection by Grant as he bombed forward at will.

The former Birmingham star even forced the first of a number of uncomfortable saves from Foster, with a rising near-post drive after his own cross had come back to him off Obinna.

At the other end, Craig Gardner sidefooted straight at Robert Green from 20 yards and that was as good as it got for the Blues before Noble pounced in the 13th minute.

The midfielder's run and cross found Obinna, whose header was cleared off the line before finding its way back to Noble, who lashed in from the narrowest of angles with Foster's view blocked by team-mate Scott Dann.

West Ham, who thrashed Manchester United 4-0 in the previous round, should have added to their tally before half-time.