The Premier League leaders actually took the lead at the Emirates through Eddie Nketiah but several reserves disappointed in a 3-1 defeat.
Arsenal threw away a first-half to lead to crash out of the Carabao Cup at the third-round stage following a 3-1 defeat to Brighton on Wednesday night.
The Gunners may be flying at the top of the Premier League, but this was perhaps another example as to why Mikel Arteta will need to strengthen in the January transfer if his side are to continue to challenge Manchester City for the title.
Arteta rang the changes for the game, with William Saliba the only player included in the starting XI who started the 1-0 win at Chelsea on Sunday.
And several of the Gunners' second string failed to take their opportunity to impress, with the likes of Fabio Vieira, Marquinhos and Sambi Lokonga struggling to make any sort of impression.
Reiss Nelson and Eddie Nketiah did catch the eye and it was the two academy products who combined for Nketiah to open the scoring in the first half.
But a mistake from 20-year-old goalkeeper Karl Hein on his debut gifted Brighton an equaliser through a Danny Welbeck penalty and second half goals from Kaoru Mitoma and Tariq Lamptey gave the visitors a deserved win.
GettyThe Winners
Winner: Reiss Nelson
The winger was Arsenal's stand-out performer in attack. While his team-mates struggled early on, he was the one player who looked confident and like he could make something happen. So, it was no surprise that when the opening goal did come, Nelson was at the heart of it, running from deep to open up Brighton before playing an excellent ball into the path of Nketiah. You could see the confidence ooze out of Nelson after that – it was just a shame a number of his team-mates weren't operating on the same level.
Winner: Eddie Nketiah
The Arsenal striker just loves the League Cup. After failing to score in his last four Europa League starts, Nketiah went into this one needing a goal and so he will have been delighted with his 20th-minute strike. The curling finish from Nelson's finish was reminiscent of the great Thierry Henry and it was 11th League Cup goal in 12 appearances. Having been asked to be on the left wing on his last two starts, Nketiah looked so much more comfortable back in his natural position as the central striker. He was a constant threat and only a couple of fine saves by Jason Steels after the interval stopped him adding more to his tally.
AdvertisementGettyThe Losers
Loser: Fabio Vieira
The Portuguese playmaker endured a miserable night. After a bright start to his Arsenal career, Vieria has really struggled of late, failing to make any sort of impact in the latter stages of the Europa League group stage. This was another opportunity for Vieira to make his mark, but instead he had a bit of a horror show. Physically, he struggled with some of the challenges that came his way and he failed to really get into the game at all. When he did get on the ball, his passing was poor and his little flicks and touches never really came off. It was just a night to forget for the Porto man.
Loser: Sambi Lokonga
Like Vieira, this was another big opportunity to impress for Lokonga. With each game that passes the young Belgian midfielder by, questions about whether he has what it takes to succeed at Arsenal continue to grow. He is clearly a good player and he is neat and tidy in possession, but he has yet to show he has the personality to take a game by the scruff of the neck at either end of the pitch. Arteta used him in a more advanced midfield role against Brighton, as he did against Zurich last week, but he never really looked like making things happen in the final third. He had one good chance early in the second half, which he dragged wide of goal. It was a finish that summed up his night.
Loser: Karl Hein
When he went to bed last night, the 20-year-old keeper would no doubt have had a few nightmare thoughts running through his head about what could happen on his Arsenal debut. And unfortunately for Hein, one of those scenarios played out in the first half when he slipped over as an overhit through ball was rolling towards him. That slip allowed the onrushing Danny Welbeck to get to the ball first and Hein then added to his error by jumping in and bringing down the Brighton striker. It was a blatant penalty and proved to be the catalyst for Brighton's comeback.
GettyArsenal Ratings: Defence
Karl Hein (4/10):
Gifted Brighton their equaliser. Occasion got the better of him.
Cedric Soares (5/10):
First start of the season, looked understandably rusty.
Rob Holding (5/10):
Struggled with Welbeck all evening.
William Saliba (7/10):
Arsenal's best defender by a distance.
Kieran Tierney (6/10):
Couple of good runs forward, but didn't lead to anything.
GettyMidfield
Mohamed Elneny (6/10):
Typical Elneny performance. Neat and tidy, but that's about it.
Sambi Lokonga (4/10):
Missed a big chance at 1-1. Another opportunity to impress gone.
Fabio Vieira (3/10):
Shocking display. Never in the game. Really poor.