Obinna delivers timely hat-trick just ahead of Keane signing

West Ham signed one international striker in Demba Ba last week and another after yesterday's game in Robbie Keane, so Victor Obinna's match-winning hat-trick against Nottingham Forest could not have been better-timed.

Keane will sign, initially on loan, with the deal being made permanent for a further two years at an estimated cost of £6m if West Ham succeed in avoiding relegation. He joins Ba, Frédéric Piquionne, Carlton Cole and Obinna in a battle for forward places at Upton Park. That probably leaves Obinna, 23, the Nigeria striker on loan from Internazionale, some way down the pecking order, but at least his treble was a reminder to Avram Grant, his manager. "He's a good talent, great quality," Grant said. "He's young and hasn't played too many games over the last year, but he's getting better and better as I expected him to be."

But if Obinna was the hero, the rest of a much-changed team also found reserves of determination that has not always been present this season. Few would have been surprised if West Ham, bottom of the Premier League, had lost to a promotion-chasing Forest team only five league places below them. Instead, Grant's men fought back from a 2-1 deficit to give their supporters some consolation for their defeat by Birmingham City in the Carling Cup semi-final in midweek.

"It was a good response," he said. "We didn't play well in the first half, but the reaction to this also was good."

But although Grant was pleased with a home draw against Burnley in the fifth round of a competition in which he seems as lucky as he has been ill-starred in the league, he acknowledged that his focus is on imminent matches against Blackpool and Birmingham. "Of course our target is the league, and the most important thing is that," he said.

Both managers made enough team changes to confirm that their priorities lay elsewhere, but Forest had the better of an entertaining first half, even if it began badly for them – Mark Noble hit a shot that was going about 10 yards wide until Obinna stuck out a foot to divert it past goalkeeper Lee Camp.

West Ham, though, have seldom defended leads with any comfort this season, and Forest were level after 18 minutes. David McGoldrick's flick was clever, but it opened up the right side of West Ham's defence far too easily, leaving Dele Adebola free to slide an angled shot past Robert Green.

That, as usual, was the signal for a crisis of confidence in the home side. Passes went astray, needless fouls were committed, pressure was invited and it was inevitable that Forest would score again. After 40 minutes, Piquionne, attempting to clear Chris Gunter's free-kick from the right, produced a glancing header that looked an own goal all the way. Green managed to get a hand to it, but only scooped it up into the air, McGoldrick nodding home from a yard out.

Just as Upton Park was drawing breath for a half-time chorus of jeers, Obinna scored a remarkable equaliser. Charging down the right, he looked up in search of a team-mate. Seeing no-one, he simply let fly and the ball sailed over the outstretched arm of the surprised Camp and into the far corner.

The scorer's slightly embarrassed reaction suggested it might have been a wayward cross rather than a brilliant shot. But his celebration was far more flamboyant seven minutes into the second half as he completed a hat-trick with a confident penalty after Joel Lynch felled Winston Reid.

Now it was West Ham who looked dangerous in every attack. Camp blocked a rocket from Piquionne, fingertipped a curling shot by Pablo Barrera round the post, and clawed away a corkscrewing effort from distance by Freddie Sears.

Billy Davies, the Forest manager, was pleased with his team's performance in the first half and, you suspect, relieved to avoid slotting a replay into a congested fixture list. "It's nice to come to the Academy of Football and play the way we did in the first 45 minutes," he said. "The England manager was here, and I don't pick his side, but Lee Camp showed some wonderful saves."

But Davies's satisfaction was nothing compared to that of David Gold, the West Ham co-owner, in confirming the signing of Keane. "We have brought in a midfielder in Gary O'Neil, a good player, and we have brought in Demba Ba and of course Robbie Keane," Gold said. "We are in a much, much better place today than we have been all season, whether it is the management structure, the board or the players. I think this is the best place we have been."

West Ham United (4-4-2): Green; Jacobsen, Reid, Gabbidon, Ilunga; Sears, Noble (Boa Morte, 74), Kovac, Barrera (Hines, 89); Piquionne (Nouble, 86), Obinna. Substitutes not used Boffin (gk), Tomkins, Parker, Bridge.

Nottingham Forest (4-2-3-1): Camp; Gunter, Morgan, Chambers, Lynch; McKenna (McCleary, 77), Cohen; McGoldrick, Majewski (Tyson, 68), McGugan; Adebola (Earnshaw, 65). Substitutes not used Smith (gk), Moussi, Moloney, Rodney. Booked Gunter.

Man of the match Obinna

Referee M Oliver (Northumberland).

Attendance 29,287.