Holders Arsenal have bowed out of the FA Cup in the fourth round in disappointing fashion, as Gabriel's first-half own goal condemned them to a 1-0 defeat by Southampton.
The Gunners' defence of the trophy they won by beating Chelsea last August ended with something of a whimper, as Mikel Arteta's side struggled with repeatedly sloppy defending.
Southampton deservedly took the lead in the 24th minute, when Kyle Walker-Peters drilled a low cross into the area and Gabriel inadvertently touched it past keeper Bernd Leno.
Arsenal could have fallen further behind, with home striker Danny Ings going close for the hosts on several occasions.
The visitors applied second-half pressure, but Southampton comfortably held on to set up a fifth-round clash with Wolverhampton Wanderers.
Southampton achieved their first FA Cup win over Arsenal and their first win over the Cup holders since 1902.
"We had, in the first half, more punch and more power," Southampton manager Ralph Hasenhuttl says. "In the second half, it's normal they have a lift.
"We must make the second goal. We made one or two chances - Shane Long should have got a penalty.
"It was a good team performance today."
Southampton are joined in the last 16 by top-flight rivals West Ham United, who crushed third-tier Doncaster Rovers 4-0, Brighton & Hove Albion, who beat Blackpool 2-1, and Sheffield United, who edged Plymouth Argyle 2-1.
Championship high-flyers Swansea City thrashed Nottingham Forest 5-1 and could face Manchester City next, if Pep Guardiola's side beat fourth-tier Cheltenham Town. Norwich City lost 1-0 at Barnsley.
With a busy Premier League spell coming up, including another trip to Southampton midweek, Arteta made some changes, with the likes of Alexandre Lacazette, Bukayo Saka and Thomas Partey among those on the bench.
Pierre-Emerick Aubameyang was also missing from the squad for personal reasons.
But that was no excuse for a lacklustre first half in which Southampton's pressing game proved too much for the visitors.
Southampton's goal was a case in point. Arsenal's Mohamed Elneny was hounded into conceding possession, Southampton then switched play to the right, with James Ward-Prowse feeding Walker-Peters, whose cross was diverted in by a sliding Gabriel.
Arsenal hadn't conceded a goal since Boxing Day.
Ings hit the woodwork shortly after the break, although his effort would have been offside, before Arsenal finally began to offer attacking threat.
Arteta sent on Partey, Saka and Lacazette, and shortly afterwards, Rob Holding side-footed their best chance over the bar, when a cross from Hector Bellerin fell kindly for him.
Eddie Nketiah blazed a late chance wide for Arsenal to leave Arteta frustrated at a first loss in seven games.
"Really sad to be out of the competition," the Spaniard says. "Disappointed to be out and the way we conceded."
Late goals spare Man City blushes
Meanwhile, late goals by Phil Foden, Gabriel Jesus and Ferran Torres have spared Manchester City a shock FA Cup defeat away to fourth-tier Cheltenham, as the Premier League giants scraped into round five.
Alfie May's 59th-minute goal put Cheltenham agonisingly close to the biggest win in their history on a night of drama at a sadly empty Jonny-Rocks Stadium.
With less than 10 minutes left on the clock, Foden volleyed in an equaliser and Jesus struck three minutes later to end the hopes of a side 72 places lower than City in the standings.
Torres gave the scoreline a comfortable look with the final kick of the game, but it was anything but.
City won their 10th straight in all competitions, but Cheltenham depart the competition full of pride, after pushing City's slickers to the limit.
City's reward is an away tie against Swansea City.