Slaven Bilic rued West Ham's inability to capitalise on a bright start as they were beaten 2-0 by Everton at Goodison Park on Sunday.
The Hammers were the better side in the opening 25 minutes and went close through Pedro Obiang, Dimitri Payet and Manuel Lanzini.
But after failing to score, Everton responded and secured victory through second-half goals from Romelu Lukaku and Ross Barkley.
"I am disappointed because we should have taken something," Bilic to Sky Sports. "I am not saying they didn't deserve it, they were more mature when the game was in the balance, but we should have done better, especially after the start we had for the first 20-25 minutes.
"We were much better and should have built on that. When we offered them a little they took it straight away, they offered us a lot, in the first half especially, but you have to be more cruel and penetrate better and score goals. If you don't score you have a big chance of losing the game."
The Hammers boss was also disappointed that his side did not manage to clear the ball before Lukaku made it 1-0.
After Adrian saved from Seamus Coleman, there were a couple of defenders in close proximity, but they were beaten to the rebound by Yannick Bolasie, who crossed for Lukaku to finish.
"We had chances to clear the first goal," said Bilic. "It was a good save from Adrian then we had a chance to clear, we didn't, we waited too long.
"We had the ball at our feet, if you concede like that you have to say it's very cheap."
Despite his disappointment, Bilic praised the performance of Lukaku, who scored his ninth goal in his last nine matches against West Ham.
"He is a world-class player," Bilic added. "Until 2-0 we coped with him really well but he is a world-class player and he is always doing that against us."