Manchester United did not show the right attitude in their surprise Premier League defeat at Brighton, says captain Paul Pogba.
The Seagulls, who beat Jose Mourinho's side at the Amex Stadium in May to retain their top-flight status, stunned their visitors by scoring three goals in the first half.
Glenn Murray flicked in the opener before Shane Duffy stroked home two minutes later.
Romelu Lukaku halved the deficit 11 minutes before the break, rising unmarked to nod in Luke Shaw's ball, but Pascal Gross converted a penalty after a foul by Eric Bailly.
Pogba also scored from the spot - deep in second-half stoppage time - but it was not enough to deny Brighton a famous win.
"The attitude that we had was not like we wanted to beat them. They had more anger than us and that showed on the pitch," Pogba told Sky Sports.
"I put myself first. My attitude wasn't right enough. We'll keep trying and keep pushing and obviously it's a lesson for us."
Mourinho said he would not blame individuals, despite admitting his side made "incredible mistakes".
The Portuguese has previously singled out players for criticism if he felt they performed below expectations but said his side were not good enough as a collective against Brighton.
"We were punished by the mistakes we made," he said. "For me that's the story of the game.
"We made incredible mistakes in some crucial moments. Mistakes that killed us."
Mourinho had a frustrating summer in the transfer market
Mourinho warned in the summer that his side faced "a difficult season" if they did not strengthen before the transfer window closed.
He had highlighted his team's defence as an area that needed bolstering, but deadline day passed without any new arrivals.
Mourinho's concerns were laid bare here, with his defence caught out on a number of occasions by Brighton's quick movement.
Bailly, in particular, struggled. Aside from giving away the penalty he also miscontrolled a pass in the second half that momentarily put March through before the Ivorian was able to recover.
Bailly and centre-back partner Victor Lindelof - both Mourinho signings - have now been a part of a defence that has conceded four goals in the first two games of the season. It took United nine to let in that many last season.
Brighton's home form played a huge part in their survival last season, with 29 of their 40 points secured at the Amex Stadium.
Once again, it looks like a trip to the south coast will be a difficult one for their Premier League rivals.
United may have been well below par but that should not take away from what was a controlled and confident display by the Seagulls against a side that finished second last season.
They took the game to their opponents from the outset, March working the defence with an early cross, and even the loss of influential defender Lewis Dunk did not disrupt them as Anthony Knockaert got in behind before putting his shot just wide.
Brighton did not have a shot after the break, but they did not need to as they changed tack from attack to containment. In the end it was a comfortable afternoon for Chris Hughton's side.
"I thought we were very good. It was a victory we deserved," said Hughton.
"There's not a player that didn't play well. To get that result with the quality they have you have to put in a good performance."
Martial managed just one shot, which was blocked, and two crosses before he was substituted
Alexis Sanchez was a surprise absentee from United's starting XI, with Mourinho confirming before kick-off that the forward was injured.
That meant Anthony Martial, who has been linked with a move, was handed the chance to impress.
Mourinho was critical of Martial for his performance here in May, and another ineffective display will surely not have impressed his manager.
Martial lasted until the hour mark before he was substituted with neither he nor Mourinho appearing to acknowledge each other as he went down the tunnel.
Solly March was everywhere for Brighton - particularly in the first half - and provided a brilliant cross for Glenn Murray's opener
Brighton travel to Liverpool on Saturday, 25 August (17:30 BST) while United host Tottenham on Monday, 27 August (20:00 BST)