Sam Allardyce admitted a poor second-half performance cost West Ham United dear in Saturday's 3-1 Barclays Premier League defeat at Norwich City.

The Hammers looked to be in control and on the way to a valuable three points at half-time courtesy of Ravel Morrison's 32nd-minute goal, with Big Sam's side dominant in almost every area during the opening 45 minutes.

After the break it was a completely different game, with Jussi Jaaskelainen's mistake allowing Gary Hooper to level emphatically with a 54th-minute penalty. Robert Snodgrass then scored with a direct free-kick after James Collins had fouled Jonny Howson before Leroy Fer wrapped up the home victory in added time.

"All the West Ham fans who travelled to Norwich have seen us play away all season with a fantastically resilient record, conceding one goal at Hull City from a penalty that should have been a penalty," said Big Sam. "Then we put in a performance in the first half here and completely dominated the game and finally got the goal we were searching for to give us the platform to go on and get three points rather than drawing.

"Our defending then threw it away from our point of view, rather than actually showing that resilience yet again to gather the three precious points we should have won.

"The disappointed lies in the fact that when the opposition beats you because they have been better than you, you accept that, but when you have gifted the opposition three points that is so difficult to take based on our first half performance."

Big Sam admitted that Norwich's penalty early in the second half altered the course of a game his team should have won. The spot-kick was awarded when Jaaskelainen dropped a routine catch and then tripped Hooper as he tried to retrieve the situation. However, replays suggested that the Finn may have got to the ball first.

"It was a soft one but at the end of the day there was contact from Jussi's arm and the player has made the best of it and the referee has seen it as a penalty," observed Big Sam. "So you could say you have seen them given and you've seen them not given.

"The bottom line is that Jussi doesn't normally make that sort of mistake and you'd hope he would get away with it, but this time he didn't get away with it and it resulted in a penalty. He shouldn't have gone diving for the ball, but because he knew he had made the mistake, he got over-anxious trying to put it right and ended up making another mistake by sadly giving the penalty away.

"What really surprised me was that it seemed to kill the spirit of the team for a bit and then we recovered from it. We then conceded a second goal which was another blow for us. Snodgrass put the free-kick, which was the fourth one against us in eleven games this season, when in two years previously at West Ham I haven't had four scored against me. That's a bizarre stat because Leighton Baines and Jermaine Pennant haven't scored one since and it will probably be a while before Snodgrass gets another one.

"He got it when it mattered for Norwich and it was a killer for us."

The manager also offered his opinion on why West Ham dominated the opening half but failed to reach the same heights after the interval.

"The first error by Jussi gave them the massive lift they were looking for and we gifted them the boost of confidence that they were searching for but looked like they were never going to get. It's a psychological thing in that it lifted the crowd. They were booing at half-time but ten minutes after, they were cheering, which makes a massive difference and that was our fault.

"We gifted Norwich three points and made life difficult for ourselves when we shouldn't have done, but there we are. We've faltered in our defensive side for the first time this season when we were one-nil up and ended up with no points when you'd have thought at half-time that we'd be stood here with a very valuable three points.

"Had the game gone on at one-nil for another ten or 15 minutes I think we would have been stood here saying we'd won two-nil because they would have got more and more desperate, thrown more and more men forward and lost their confidence. That would have given us more chances to add a second, but unfortunately it didn't pan out that way and we only have ourselves to blame."