Match ends, Brighton and Hove Albion 0, Southampton 2.
Brighton manager Graham Potter said he "can't defend" Florin Andone's challenge which resulted in the Romanian's dismissal in the Seagulls' 2-0 defeat to Southampton.
Andone was shown a straight red card on the half-hour mark following a high, rash challenge on Saints defender Yan Valery.
The hosts had looked comfortable up to that point, with Neal Maupay and Martin Montoya going close to breaking the deadlock in the first half.
However, a sumptuous strike from Moussa Djenepo - moments after the Malian had come on as a substitute - and a late Nathan Redmond goal secured the points for Ralph Hasenhuttl's side.
"It didn't look like a great tackle," Potter told Match of the Day. "That's not a tackle we want to see. I don't think he's meant to do it, but it's one we can't defend.
"We tried to be positive with 10 men, but it was a tough task against a good Southampton team.
"We're at the start of this process together. It's about how we react to these moments and situations."
Lewis Dunk thought he had given the hosts the lead eight minutes after Andone's sending off, only for the goal to be ruled out for offside against defender Dan Burn.
Substitute Jurgen Locadia struck the post for Brighton late on, but Redmond slid home Sofiane Boufal's cross in second-half stoppage time to seal the win for the away side.
Seagulls fade following Andone dismissal
After narrowly avoiding relegation last season, Brighton have made a solid start to life under former Swansea City manager Potter.
An eye-catching 3-0 opening-day win at Watford was followed by a 1-1 home draw with West Ham, in which summer signing Leandro Trossard delivered a man-of-the-match display.
The Belgian was heavily involved early on at the Amex Stadium, teeing up Maupay whose tame effort was easily held by Southampton goalkeeper Angus Gunn.
The 24-year-old's in-swinging cross was headed wide by Montoya soon afterwards as Potter's side continued to turn the screw.
However, the game swung the visitors' way when Andone was dismissed following a rash challenge that left Valery writhing in agony near the halfway line.
The Seagulls responded well initially, with Dunk's header chalked off by VAR, but Southampton capitalised on their numerical advantage in the second half.
Potter's side almost equalised moments before Redmond's strike when Locadia latched onto Glenn Murray's flick-on, but the Dutchman sliced his effort against the frame of the goal as the Saints inflicted a first defeat on the new Brighton boss.
Djenepo's instant impact
Southampton responded to their 3-0 reverse at Burnley on the opening day with a much-improved performance in defeat to Liverpool last weekend.
Hasenhuttl's side matched the European champions for large parts at St Mary's but failed to take their chances, with Danny Ings missing a glorious opportunity to equalise in second-half stoppage time.
At the Amex Stadium, the Saints failed to register a shot on target prior to Andone's red card, despite seeing plenty of the ball.
Indeed, the closest they came to a breakthrough in the first half was when Redmond's low shot from the edge of the box was held by Mat Ryan.
Djenepo, who made his debut for the club against Liverpool last weekend, replaced Valery eight minutes into the second half and his impact was almost instant, cutting in from the left and curling into the top corner just two minutes after entering the fray.
Second-half substitute Stuart Armstrong was thwarted by Ryan late on, but Redmond's strike - following fine play by Boufal - sealed the win as Southampton secured their first Premier League clean sheet since their 1-0 victory at Brighton in March.
Man of the match - Nathan Redmond (Southampton)
Saints continue dominance over Seagulls - the stats
- Southampton have won each of their last three away games against Brighton in all competitions, keeping a clean sheet each time.
- Brighton have scored just eight goals in their last 14 Premier League home games, and never scored more than once in a match in that run.
- Three of the last four Premier League red cards shown by referee Kevin Friend have been to Brighton players (Shane Duffy v Crystal Palace, Anthony Knockaert v Bournemouth and Florin Andone today).
- Moussa Djenepo's goal for Southampton - his first in the Premier League - came with his first touch in the match and just 78 seconds after coming on as a second-half substitute.
- No player has scored more Premier League goals for Southampton under Ralph Hasenhuttl than Nathan Redmond (7).
- Southampton's Danny Ings has been directly involved in three goals in his last four Premier League games (1 goal, 2 assists), more than he had in his previous 11 in the competition (2).
'The red card made it difficult' - what they said
Brighton manager Graham Potter, speaking to Match of the Day: "We started really well and created some opportunities. The red card made it difficult for the rest of the game.
"We started the second half well - we had attacks and won the ball back, but then they score.
"I was incredibly proud with the effort they put in. That's life sometimes."
Southampton manager Ralph Hasenhuttl, speaking to Match of the Day: "There's no question it was a clear red card. I'm glad Yan Valery was not injured because it looked horrible.
"Sometimes we gave the ball away too easily. After two games you have no points so you have little confidence, but I still think we could have done better. This was an important win for us.
"Moussa Djenepo is very quick and hard to defend against - in the two games he's played he's made an impact as substitute."
Brighton travel to Bristol Rovers in the EFL Cup on Tuesday 27 August (19:45 BST), before returning to Premier League action at champions Manchester City on Saturday 31 August (15:00 BST).
Southampton play Fulham at Craven Cottage in the EFL Cup on Tuesday before welcoming Manchester United to St Mary's in the Premier League the following Saturday (12:30 BST).
- 22MontoyaBooked at 89mins
- 6StephensSubstituted forGroßat 78'minutes
- 20MarchSubstituted forLocadiaat 68'minutes
- 7MaupaySubstituted forMurrayat 74'minutes
- 10AndoneBooked at 30mins
- 43ValerySubstituted forDjenepoat 53'minutesBooked at 62mins
- 23HøjbjergBooked at 82mins
- 16Ward-ProwseBooked at 21mins
- 10AdamsSubstituted forBoufalat 80'minutes
- 9IngsSubstituted forArmstrongat 84'minutes
- 2Cédric Soares
- Kevin Friend
- Shots on Target
Second Half ends, Brighton and Hove Albion 0, Southampton 2.
Attempt missed. James Ward-Prowse (Southampton) right footed shot from outside the box is too high from a direct free kick.
Foul by Lewis Dunk (Brighton and Hove Albion).
Sofiane Boufal (Southampton) wins a free kick in the attacking half.
Dan Burn (Brighton and Hove Albion) wins a free kick on the left wing.
Foul by James Ward-Prowse (Southampton).
Goal! Brighton and Hove Albion 0, Southampton 2. Nathan Redmond (Southampton) right footed shot from very close range to the bottom right corner. Assisted by Sofiane Boufal.
Attempt saved. Stuart Armstrong (Southampton) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Nathan Redmond.
Martín Montoya (Brighton and Hove Albion) is shown the yellow card for a bad foul.
Foul by Martín Montoya (Brighton and Hove Albion).
Moussa Djenepo (Southampton) wins a free kick in the defensive half.
Delay over. They are ready to continue.
Delay in match because of an injury Jan Bednarek (Southampton).
Jürgen Locadia (Brighton and Hove Albion) hits the left post with a left footed shot from the left side of the six yard box. Assisted by Glenn Murray following a corner.
Attempt missed. Glenn Murray (Brighton and Hove Albion) header from the centre of the box misses to the left. Assisted by Pascal Groß with a cross following a corner.
Corner, Brighton and Hove Albion. Conceded by Jan Bednarek.
Lewis Dunk (Brighton and Hove Albion) wins a free kick in the attacking half.
Foul by Pierre-Emile Højbjerg (Southampton).
Substitution, Southampton. Stuart Armstrong replaces Danny Ings.