It was a game overshadowed by a horrific injury to the away side's goalkeeper, with Bernd Leno having to be stretchered off in the first half.
Despite their expanding injury list, Mikel Arteta's side took the lead, when Nicolas Pepe finally got the best of Brighton keeper Mathew Ryan midway through the second half. Brighton didn't take it lying down, hitting back 10 minutes later when Arsenal's botched defending from a corner kick allowed Lewis Dunk to poke home.
The visitors pushed on for a late winner, but it was Brighton who stole the three points after Maupay's cool finish to a great attacking move completed a remarkable turnaround for the Seagulls.
Arsenal's young players have often led by example under Mikel Arteta's management, and today was no exception. Bukayo Saka was once again superb, this time deployed on the left side of a midfield four. He deserved a goal, but the closest he came to one was a first-half strike that cannoned back off the crossbar.
Leno's first-half injury was a real gut punch for Arsenal, who also saw a number of key players sidelined after Wednesday's c3-0 defeat to Manchester City at the Etihad. Leno's knee appeared to twist upon landing, raising concerns over what could well turn out to be a long term layoff.
After his heroics against City, he's going to be sorely missed. Arsenal's late defensive collapse will also be of concern moving forwards.
Manager rating out of 10
6 -- Arteta had few other defensive options this afternoon, with his first-choice centre-backs absent due to injury or suspension. However, the Spaniard did make the bold call of setting his side out in a makeshift 4-4-2 formation. It worked well going forward, with Saka and Pepe performing superbly from wide positions.
Player ratings (1-10; 10 = best. Players introduced after 70 minutes get no rating)
GK Bernd Leno, 7 -- Was stretchered off after a horrific knee injury in the first half. He started the game brightly, with a few key interventions and smart pieces of handling.
DF Hector Bellerin, 5 -- Was caught out of position a few times, with Brighton generally getting more joy down his right-hand side of the pitch.
DF Rob Holding, 5 -- The Englishman started off well, before faltering late on. Despite his best efforts, he couldn't keep out Lewis Dunk's close-range tap-in.
DF Shkodran Mustafi, 6 -- Solid, if unspectacular. After the troubles that Arsenal have had in defence of late, a mistake-free afternoon is just about all you can ask for from the Germany International.
DF Sead Kolasinac, 6 -- Arsenal's best defender for the first hour, contributing with a number of crucial headers, particularly from set pieces. He didn't venture forward to- much, but with Saka directly ahead of him, he also didn't need to.
MF Matteo Guendouzi, 6 -- In possession, the midfielder instinctively looked to create openings and set the tempo centrally. Committed one or two needless fouls, but overall, his defensive contribution was solid. Was heavily involved in a postmatch fracas following Maupay's late winner.
MF Dani Ceballos, 5 -- Provided sporadic moments of creativity, but at times, the Spaniard did look off the pace when making tackles. He surely would have been more effective playing in an advance's role, rather than in a midfield two.
MF Nicolas Pepe, 7 -- The Gunner's club-record singing was a constant thorn in the side of Brighton left-back Dan Burn - whom he managed to get booked early on. In the second half, he curled a shot ball beautiful past Ryan, to hand Arsenal a richly deserved lead.
MF Bukayo Saka, 7 -- Not for the first time this season, the teenager was one of Arsenal's best performers, after setting the tone early on with a beautiful strike that rattled the crossbar. Following this, he played two wonderful crosses into the Brighton box, which should have yielded an assist for the academy graduate.
FW Alexandre Lacazette, 6 -- The Frenchman showcased intelligent movement but, in dangerous areas, his end product was often wasteful. Three goal-scoring chances were presented to him, but the sharpness we're so accustomed to wasn't quite there today.
FW Pierre-Emerick Aubameyang, 7 -- Linked up well with Lacazette, whom he partnered up front. In the second period, the 31-year-old had a goal ruled out for a marginal offside.
Emiliano Martinez, 6 -- Replaced the injured Leno in the first half, and was instantly called into action, saving well from an Aaron Mooy piledriver. Can hardly be blamed for Brighton's two late goals.
Eddie Nketiah - N/A
Kieran Tierney - N/A
Reiss Nelson N/A
Joe Willock - N/A