Manchester United captain Paul Pogba admitted his side didn't have the right attitude in losing 3-2 to Brighton on Sunday due to a shambolic defensive display.
For the first time in nearly two years, Jose Mourinho's men conceded more than twice with all three Brighton goals arriving before half-time through Glenn Murray, Shane Duffy and a Pascal Gross penalty.
"They had more hunger than us. I put myself first, that my attitude wasn't right enough. We made mistakes we shouldn't make," said Pogba, whose penalty deep into stoppage time proved too little, too late.
United manager Mourinho warned of a "difficult" season when he wasn't backed in the transfer market before the deadline for Premier League clubs closed before the opening weekend of the season.
Strengthening the heart of his defence was Mourinho's priority and it showed as Victor Lindelof and Eric Bailly endured a torrid afternoon on England's south coast.
"We were punished by the mistakes we made. For me that's the story of the game," said Mourinho. "We made incredible mistakes in some crucial moments. Mistakes that killed us."
Romelu Lukaku briefly brought United back into the game at 2-1. But there was little reaction after the break until Pogba's penalty as United fell three points behind defending champions Manchester City, Chelsea and Tottenham just two games into the new campaign.
When United also lost on their last visit to Brighton in May, Mourinho lambasted those handed their chance to fight for a place in the FA Cup final in one of a series of public tirades against his players.
And he claimed the backlash he received for doing so means he won't speak his mind so freely despite his third season in charge ominously getting off to a bad start like it did at Real Madrid and his second season at Chelsea.
"Don't expect me to speak with you about it because you and your colleagues were really critical when in previous seasons I was too honest, too open analysing players performances," added Mourinho. "So don't ask me to do what you criticise so much."
- Classy finish -
The story could have been very different for the visitors had Lukaku not wasted a huge chance to open the scoring when he pulled his shot wide of the near post 10 minutes in.
Instead, Brighton went in front when veteran striker Murray caught Lindelof ball watching to flick home Solly March's cross with a classy finish.
Two minutes later, the hosts led 2-0 as Duffy was given the space to control and fire past a helpless David de Gea after United failed to clear a corner.
Despite suggesting he is unhappy at Old Trafford after scoring in last weekend's 2-1 win over Leicester, Pogba was again handed the captain's armband by Mourinho.
However, there was little sign of Pogba leading United out of the mire as he and summer signing Fred, who cost a reported �52.5 million (57.9 million euros, $66.3 million) struggled to control the game in midfield.
"I know you cannot always play very, very good," added Pogba. "The attitude always has to be very good and we missed that."
Brighton's failure to defend set-pieces cost them in a 2-0 defeat to Watford last weekend and threatened to undo their good work again when Lukaku was left unmarked just five yards out to nod home Luke Shaw's deflected cross and give United a lifeline.
That reprieve lasted just 10 minutes, however, before more rash defending by Bailly allowed Brighton to restore their two-goal lead when he brought down Gross, who converted from the spot.