Saints’ long unbeaten run at St Mary’s came to an end at the hands of the reigning champions with a 3-0 defeat to Manchester City.
All three goals arrived in the second half of the game, with Manuel Pellegrini’s men eventually overpowering a resilient Southampton side, who had kept City at bay for long periods before they made their breakthrough.
Yaya Touré opened the scoring on 51 minutes with a fierce strike that ended the hosts’ record of just one strike conceded at home this season, but it wasn’t all plain-sailing for the visitors from there.
The 74th minute dismissal of Eliaquim Mangala for two bookable offences appeared to open the door for Saints, who had tested Joe Hart throughout the contest, but the champions stood firm and delivered a performance worthy of their status to see off the hosts.
Substitute Frank Lampard effectively sealed the win on 80 minutes, but Gael Clichy made sure with another strike two minutes from time to wrap up a win which moved City above Saints in the table as Koeman’s men lost at home for the first time this season.
Steven Davis had returned for Saints and came straight back into the starting line-up in place of the benched Shane Long. The hosts were without Jack Cork through illness in the only change to the squad.
City named 17 goal marksman Sergio Agüero in attack, but made four changes to the team that started in the win over Bayern Munich in midweek with Fernandinho, Pablo Zabaleta, Yaya Touré and Stevan Jovetic all restored to the starting eleven.
Ahead of kick-off, City won the toss and elected to move Joe Hart into the shaded Chapel end, with opposite number Fraser Forster taking up residence in front of the Northam stand.
City sought to make the most of their sunlight advantage with a solid start to the contest as they tested the resolve of the Saints defence early on.
The visitors’ cause was helped by a seventh minute booking for Victor Wanyama who on first showing appeared unfortunate to see yellow for a clip on Yaya Toure, with the tone now set by official Mike Jones in a competitive period of play.
The jeers for the caution awarded to Wanyama, were silenced when Aguero went to ground two minutes later just inside the area, but Jones decided that City’s striker had dived and promptly booked the Argentine.
City upped the ante, with Toure curling a shot at Forster from distance which the keeper gathered at the second attempt, no doubt slightly hindered by having the sun in his eyes.
Saints created their best moment of the half on 21 minutes when Morgan Schneidelrin’s clipped ball into the area saw Pellè denied at point blank range, and then a low save from Joe Hart denied a shot from Davis, before a follow-up by Tadić was thwarted at close range.
City responded with a wayward strike from Aguero which cleared the bar, before Alderweireld spared Forster’s blushes when he cleared the ball off the line from Jovetic’s shot which went through the keeper.
The hosts grew into the game and saw Pellè flick a glancing header across goal and wide of the far post from Davis’s corner, with Hart alert again to deny Saints from two further set-pieces.
Toby Alderweireld stopped Aguero’s pass from reaching Jesus Navas as the clock ticked towards half-time, with Saints holding their own heading into the break.
At the interval, Schneiderlin was replaced by Maya Yoshida in what appeared to be a tactical move by Koeman, with Alderweireld moving into midfield alongside Wanyama.
It was Alderweireld who almost caught City out with an ambitious effort which went wide of Hart’s left post just seconds into the new half, before Tadić also found space on the right to hit a low strike wide of the far post.
The deadlock was broken on 51 minutes, with the visitors finally finding a way through. A cutback from Aguero on the left touchline arrived at the feet of Yaya Toure, who drilled a firm strike into the net via a slight deflection off Alderweireld to give City the lead.
A patient spell by Saints saw them soak up the pressure, including a couple of corners which flashed across the penalty area, before a flash point arrived in the 74th minute.
Substitute Shane Long burst through towards the area where he was hauled back by already booked Mangala. The City defender was duly sent off, with the visitors bringing on Martin Demichelis in place of Navas to shore things up.
Moments earlier, Navas had gone close with a low strike which went wide, with City sacrificing one of their livelier players to accommodate Demichelis.
Tadić’s free-kick from the position that Long was brought down, crashed into the wall, but Saints headed into the final quarter of an hour expected to find a way through.
It was City though, who would wrap up the success when substitute Frank Lampard smashed home from the edge of the area with a low drive that beat Forster into the bottom left of the goal.
Forster went on to save well from Aguero, but City sealed their success with a fine goal on 88 minutes when Aguero’s superb cross-field pass found Gael Clichy who rocketed a strong shot into the far corner for 3-0.
City ended the game with nine men after losing captain Kompany to injury, but it was too late for Saints to rescue the contest.
Southampton team: Fraser Forster, Nathaniel Clyne, José Fonte (c), Toby Alderweireld, Ryan Bertrand, Morgan Schneiderlin (Maya Yoshida 46), Victor Wanyama, Steven Davis (Emmanuel Mayuka 82), Sadio
Mané (Shane Long 67), Dušan Tadić, Graziano Pellè
Unused substitutes: Kelvin Davis, Matt Targett, Florin Gardos, Harrison Reed
Booked: Wanyama (7)
Manchester City team: Joe Hart, Pablo Zabaleta, Eliaquim Mangala, Vincent Komapny (c), Gael Clichy, Fernandinho, Yaya Touré, Jesus Navas (Martin Demichelis 74), Samir Nasri (Frank Lampard 65), Steven Jovetic (James Milner 54), Sergio Agüero
Unused substitutes: Willy Caballero, Bacary Sagna, Fernando, Jose Angel Pozo
Goals: Toure (51), Lampard (80), Clichy (88)
Booked: Agüero (9), Mangala (22) & (74)
Referee: Mike Jones
Attendance: 30,919 (including 2,596 away)