Kaoru Mitoma and Tariq Lamptey were both on target in the second half as Arsenal were knocked out of the EFL Cup in the third round after a 3-1 home defeat to Brighton and Hove Albion.
The Gunners faltered for just a second time in their last 20 appearances in the third round of the competition, despite dominating for large periods at Emirates Stadium on Wednesday.
Danny Welbeck's first-half penalty had cancelled out Eddie Nketiah's opener, before Mitoma and Lamptey struck in the space of 13 second-half minutes to end Arsenal's nine-match home winning run.
4 - Danny Welbeck is the first player to score at Arsenal's Emirates stadium with four different clubs (Man Utd, Arsenal, Watford & Brighton). Array. pic.twitter.com/kV1S7LjxW6— OptaJoe (@OptaJoe) November 9, 2022
Julio Enciso headed just off target before Jeremy Sarmiento fired narrowly wide but Arsenal struck in the 20th minute when Reiss Nelson found Nketiah, who curled a smart first-time finish past Jason Steele.
Debutant Karl Hein's slip offered Brighton their equaliser, though, as the goalkeeper brought down Welbeck, who coolly converted his spot-kick into the bottom-right corner.
A fizzing Nketiah right-footed drive cannoned against the left post after the interval, before Steele kept out Nelson's header with a stretching stop.
Brighton hit the front as Sarmiento danced through the middle before laying off for Mitoma to whip a right-footed effort into the bottom-right corner from inside the area.
Former Chelsea defender Lamptey sealed victory soon after as he drilled under Hein after being teed up by Billy Gilmour.
What does it mean? Gunners blunted by Seagulls
Brighton had lost all five of their all-Premier League clashes in the EFL Cup since reaching the top flight in 2017-18, but produced a resolute showing to earn another victory at Arsenal.
The Seagulls have now won three of their last four trips to Arsenal, having lost all eight of their previous visits to the Gunners between November 1979 and May 2019.
Arteta's side will be frustrated to drop out of the EFL Cup so early on but have much bigger tasks to focus on as they compete for Premier League and Europa League glory.
Welbeck scores on return again
Welbeck showed all of his experience to draw Hein into the foul for the first-half penalty he calmly dispatched by sending the goalkeeper the wrong way.
The striker became the first player to score at Emirates Stadium with four different clubs (Manchester United, Arsenal, Watford and Brighton) as he came back to haunt his former side.
Hein mistake proves costly
Hein was made to wait for his first chance at Arsenal since leaving his native Estonia to join from FC Nomme United in 2018.
But the 20-year-old goalkeeper failed to impress when called upon, with his erroneous decision to rush out before slipping to bring down Welbeck allowing Brighton a way back into the game after going a goal down.
Arsenal play their final Premier League game before the World Cup break at Wolves on Saturday, while Brighton host Aston Villa the day after.