Defender Shane Duffy said Albion's second half performance wasn't good enough after Fulham fought back from 2-0 down to claim a 4-2 Premier League win last night.
Glenn Murray scored twice in the opening 17 minutes and the Seagulls could have been further ahead at half-time. Murray was denied his hat-trick by the legs of Fulham keeper Sergio Rico and poked another effort wide, while Davy Propper also crashed an effort off the bar.
The Cottagers came out a different side in the second half and got a goal back immediately through Calum Chambers' 20-yard half-volley.
Aleksandar Mitrovic then got to the ball ahead of Duffy and keeper Mathew Ryan to make it 2-2.
Murray had a header brilliantly saved by Rico, before Mitrovic headed Fulham into the lead although Brighton felt the striker fouled Lewis Dunk as he headed home.
Lucianno Vietto nodded home the fourth for Fulham, who also hit the woodwork three times in a dominant second half display.
Duffy was at a loss to explain what happened in the second half as Albion conceded four goals in a Premier League for the first time since losing 4-0 at Liverpool in the final game of last season.
The Irishman said afterwards: "It just wasn't good enough in the second half. In the first half we dominated but in the second half we just stopped.
"At this level, you can't stop and I think maybe some players' mentality stopped. We gave them a goal straight away and they got confidence from it.
"We played well and were the best team in the first half by a mile. Glenn took his two goals well and we played some good stuff. They couldn't control it and at half-time we spoke that we had to go and get the next goal but we didn't.
"We stopped getting second balls, we stopped pressing, we sat off too deep and they punished us.
"I couldn't see it coming. It's hard at the minute to know what happened.
"We felt like they weren't even troubling us (first half), they were getting it wide and we were defending it. Maybe with the second balls we were too deep and they were playing it to Mitrovic and he's a strong boy and they play to their strengths.
"We've got to look at ourselves and put it right on Saturday."
It was the second time Albion have lost a 2-0 lead away from home this year, after drawing away at West Ham at the start of the month and Duffy said: "We know we can't win them all but this is just disappointing, having gone 2-0 up.
"It's the second time now we've done it and we've got to sort it out because it can't keep happening.
"That could have been six points, so it's something we've got to do mentally or something. Players need to go out there and be strong and try and see it through."
Brighton now have back to back league games at the Amex against Watford and Burnley and Duffy said: "They're all big. This was massive for us. It's not been our night and every game is massive. The next couple are at home, so we've got to look to get back to winning ways.
"We know every game is important and we knew if we beat these tonight we could get further away but we haven't.
"This is this league. It's difficult at times.
"We knew in the second half they had to go for it as they had nothing to lose.
"They went for it and we couldn't deal with it.
"We've got to have a look at it and get back to the drawing board."
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