Nigel Adkins says Southampton's latest defeat was hard to take after they had frustrated West Ham before half-time.
The South Coast side had looked comfortable in a goalless first 45 minutes, but two goals after the restart for the hosts put the Hammers firmly in control.
Adam Lallana gave Adkins' side hope, but a Mark Noble penalty put daylight between the two recently-promoted sides before Modibo Maiga's superb curled effort late on put the result beyond any doubt.
"The first half was pleasing, we passed the ball well and kept the crowd quiet," said Adkins. "We kept a high line, defended well and at half-time I felt we had a great opportunity to get a win.
"Lo and behold, within a couple of minutes of the second half starting we were two down. We had to regroup, which we did, and the lads played a little bit of football with Lallana scoring a very good goal.
"With Lambert and Mayuka on, we were in the ascendency and I felt there was an opportunity to go on and win the game. But the penalty killed us, it took the stuffing out of us and they went on to win the game. It's hard to take."
The Saints have now shipped 24 goals in eight games since returning to the Premier League, and Adkins feels the defeat to West Ham was scant reward for their efforts in trying to shore up their defences.
"The lads worked really hard in training this week, and the first half performance was good," he added.
"We won the headers and the knock-downs, kept good possession and looked threatening. It's frustrating, one minute you feel you have an opportunity, the next you are two goals down."
Mark Noble's penalty, awarded after Jose Fonte's handball, was the killer blow for the former Scunthorpe boss.
"We were on the front foot, looking threatening again. The ball came into the area, there were a lot of people jumping, arms all over the place, it hit one and the referee gave the penalty. That, ultimately, took the sting out of us.
"They (the players) have to pick themselves up, we have to pick them up and the football club has to pick itself up. We have to get ready to go again."