West Ham manager Slaven Bilic described himself as "gutted" to suffer defeat at 10-man Southampton in the Premier League on Saturday.
Victor Wanyama was sent off in the second half, but the Hammers were unable to recover from Maya Yoshida's early goal as they missed the chance to move above Manchester United in fifth with a 1-0 defeat.
That was only West Ham's second loss in their last 12 league encounters and Bilic was critical of the way his team started the game and then failed to take advantage of their numerical advantage later on.
He told Sky Sports: "You can lose a game but when you lose a game like this, we are gutted.
"I would like to congratulate Southampton, they fought and they were very good in defending the box so they deserve it.
"It was one of those defeats that is really hard to take and it was down to - I said this to the guys in the dressing room at half-time - the first 15 minutes. We basically gave them a couple of corners unnecessarily, they were better on the second balls, they were better in the first 15 minutes.
"We started better in the second half and then when they were with 10 men we were dominating and all that but we didn't create enough. Our crosses were quite poor or they defended really well."
Bilic did not think there was any debate about referee Mark Clattenburg's decision to send off Wanyama for a challenge on Dimitri Payet that he felt was unacceptable.
"It didn't turn out to be a key moment because it was 1-0 at the end, but it was a red card," added the former Croatia boss.
"He didn't get Dimitri but my opinion is - sliding is a great part of the game - but when that second leg comes and you do scissors it is so dangerous. It was a reckless challenge from their player so for me it was a red card."