West Ham United boss David Moyes was left frustrated after a 'soft' second-half display against Arsenal at the Emirates Stadium on Boxing Day.
Said Benrahma gave the Hammers the lead from the penalty spot, after William Saliba was adjudged to have fouled Jarrod Bowen.
But Bukayo Saka levelled soon after the restart and Gabriel Martinelli fired the Gunners in front soon after.
Eddie Nketiah's fine finish sealed a 3-1 win for the Premier League leaders, leaving the Hammers one point above the relegation zone.
And Moyes said: "We were resolute in the first half. We did things we are actually quite good at and have been over the last few years that we can be tough and hard to beat.
"We did that but we didn't do that in the second half.
"Arsenal played well in the first half, probably played as well in the first half as they did in the second half but we get soft in the second half and gave them opportunities to score."
The visitors might have gone 2-0 up early in the second half, but Aaron Ramsdale denied Michail Antonio on a counter-attack.
Saka then slotted past Lukasz Fabianski when Martin Odegaard's mishit shot fell at his feet and Martinelli drove a low shot past the Polish keeper at his near post just five minutes later.
Nketiah spun away from Thilo Kehrer to drive an angled shot inside the far post to seal the points and Moyes added: "We defended really poorly and made big mistakes in the second half.
"We've got really unfortunate the first goal. The boy comes inside and should have never been allowed the chance because we had a chance to break on them, then Odegaard gets a chance to come inside and shoot and it just all felt too easy.
"I have to say a few decisions went against us just after half-time. Maybe around 50 minutes two or three decisions went against us which didn't help the momentum of the game.
"There were some things which hopefully will work for us in the games to come, but we've got to make sure we get back to being tough and hard to play against and we were for about 50 minutes."
West Ham welcome Brentford to London Stadium for their final fixture of 2022 on Friday and Moyes says they need to create a positive atmosphere.
He added: "We need to do it, the players need to do it and get a result, as that gets the crowd going.
"All the momentum built up over the last two years is because of the results we've had and that's why the stadium was the way it is, or has been, so we have to find a way of getting the results."
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