Despite having Joao Cancelo sent off just 10 minutes in, the visitors led 2-0 thanks to an Ilkay Gundogan header and a superb Phil Foden goal, prior to the unexpected capitulation.

City boss Guardiola, whose team will lift the Premier League trophy after hosting Everton on Sunday, says the uncomfortable experience provides plenty to work on ahead of arguably the biggest game in the club's history.

"Eleven against 11 against Brighton is tough, 11 against 10 is difficult so we have to improve for the final," said the Spaniard.

"Unfortunately after 0-2, we conceded a goal so quick and after they push a lot, we were more tired and could not keep the ball as much as possible, we could not do it and unfortunately we lost the game – congratulations Brighton.

"On Sunday, with our people, we are going to lift the trophy. And after we are going to go for the final of the Champions League.

"I am concerned because this is the final of the Champions League, because the opponent is so tough.

"I saw incredible things today in the pitch with 11 against 10 for 80 minutes in the Premier League.

"We are fortunate to lift the (Premier League) trophy and we did it ourselves. Nobody gave us absolutely anything; nothing.

"That's why I am so proud of the team; it means how difficult is the Premier League again, and now we're going to prepare as best as possible for the final of the Champions League."

City were on course for a 13th-successive top-flight away win after Gundogan nodded the early opener but the momentum swung 10 minutes in when Cancelo was dismissed for denying Danny Welbeck a goal-scoring opportunity.

Foden's fine individual effort doubled the advantage just after the restart but an error from Rodri allowed Trossard to swiftly halve the deficit and defenders Webster and Burn added further punishment.

Influential stand-in skipper Gundogan, who claimed his 13th Premier League goal of the campaign, went off injured in the second period, although Guardiola remains hopeful the issue is not too serious.

"Tomorrow, we are going to check tomorrow," said the manager.

"The doctor is quite optimistic. The problem is a kick and he was running in the second half with disruption and I didn't want to take a risk."

Brighton's sensational success was a first in eight Premier League attempts against City.

Seagulls head coach Graham Potter soaked up the acclaim of the euphoric 7,945 returning supporters, leading a richly-deserved lap of honour at full-time.

After playing behind closed doors for most the past year, Potter says building a close bond between fans and players is the "most important connection".

"They're the best team in the world and the boys had to stick in and carry on and I am just so pleased for them that they get an evening like this in front of the supporters," he said.

"The most important connection is between the supporters and the players at the football club and I think tonight would have helped that.

"The supporters were great with us, really, really good and in the end it was a fantastic game of football.

"It's been a tough year. We've suffered a lot, playing in empty stadiums, as has everybody. I think 'emotional' is a good word to describe the feeling in the stadium.

"I thought the players gave everything, it was incredible. They put in a really top performance and I think the crowd appreciated it."

An unforgettable night for the Sussex club was slightly marred by a first-half injury to Welbeck, who is now expected to be absent the weekend to trip to one of his former clubs, Arsenal.

"I've not had an update from the medical. He's felt his hamstring," said Potter.

"Disappointing for him, looks like he will miss Arsenal but we will see how bad it is."