Match ends, Southampton 0, Manchester City 3.
Manchester City strengthened their hopes of a top-four Premier League finish as a slick second-half display saw off a subdued Southampton.
Injury-hit skipper Vincent Kompany headed David Silva's left-wing corner past keeper Fraser Forster's weak save for his first goal in 20 months.
Leroy Sane drilled in Kevin de Bruyne's pass after a quick counter, with Sergio Aguero's far-post header sealing it.
Pep Guardiola's side are third, seven points clear of fifth-placed Everton.
Mid-table Saints failed to create many chances against a City side well marshalled by Kompany, with Dusan Tadic shooting over before the break.
Claude Puel's side, who were attempting to win three successive league games for the first time under the Frenchman, remain in ninth place.
Good Kompany for City
How would City's season have panned out had they had a fully fit Kompany playing regularly?
Many Blues fans would suggest their team would be much closer to leaders Chelsea - and, on the evidence of his performance against Southampton, it is hard to disagree.
City's talismanic captain has made just eight appearances in another campaign limited by niggling injuries, but returned at St Mary's with an imperious display.
While Kompany will grab the headlines for his goal, his work at the other end of the pitch - leadership, organisation and composure - is what the Blues have been lacking at times this season.
City's defensive resilience meant keeper Claudio Bravo - trusted again by Guardiola - barely had to make a save.
And it laid the platform for the visitors to cut Saints apart once Kompany, who marked his goal with an exuberant celebration, had made the breakthrough.
"I scored in front of the away fans and for me it was a great feeling," the Belgian said.
"I feel like I want to give so much but I am restrained at times. I keep positive and keep going no matter what."
Slick City looking good for top four?
Guardiola might have thought winning the Premier League during his first season in English football would be relatively straightforward after starting with seven successive wins.
Instead, the Spaniard goes into the top-flight run-in facing a tense wait to see if his team are good enough to finish in the top four.
If City play with this sort of defensive resilience, in conjunction with their already lethal attacking play, it will be hard to see either Everton or Manchester United overhauling them.
Once the visitors took a deserved lead, they looked resolute at the back and picked off Saints on the break with a clinical counter-attack to double their advantage.
De Bruyne led the charge as City broke quickly, expertly picking out Sane for the young German to drill low under Forster.
De Bruyne was also the architect for the third, clipping a right-wing cross to the far post for Aguero to secure City's first win in four away matches.
"This result is so important for our qualification for the Champions League," said Guardiola, whose side host neighbours United in their next league game.
"It will go to the last game for the Champions League. It will be so tough."
Saints marching on... to a mid-table finish
Southampton look almost certain to fall short of emulating last season's sixth-place finish as Puel's first campaign at the helm is petering out to a quiet conclusion.
Saints will need a remarkable finish to grab European qualification and, having already passed the 40-point mark deemed enough to avoid relegation, are well clear of the drop.
Their performance against City was indicative of a side with little to play for going into the final month of the season.
The home side only managed one effort on target, and Maya Yoshida's second-half header was easily stopped by Bravo.
"We simply did not play well enough, we were nervous with the ball," said Puel, who replaced Ronald Koeman last summer.
Man of the match - Vincent Kompany (Manchester City)
City's attentions are diverted away from the Champions League chase and onto the pursuit of silverware as they meet Arsenal in the FA Cup semi-final next Sunday (15:00 BST).
Guardiola's side return to Premier League action when they host neighbours United on Thursday, 27 April (20:00).
Saints have a 10-day break before returning with a trip to leaders Chelsea on Tuesday, 25 April (19:45).
No away-day Blues....
- City have won 11 away games this season, more than they have in any other top-flight campaign.
- Guardiola has made 100 changes to his Premier League starting line-ups this season, 15 more than any other manager.
- Since his debut in August 2010, Silva has provided 64 Premier League assists - 13 more than any other player.
- De Bruyne is the Premier League's leading assist maker this season, having set up 13 goals.
- Sane has scored in three of his past four Premier League away games.
- Aguero has scored in each of his past 12 Premier League appearances in the month of April
Manchester City manager Pep Guardiola: "I missed Vincent Kompany a lot. He wins duels, he can find passes to help us, so hopefully he can be fit until the end of the season because he's important for us.
"With all the injured players, Gabriel Jesus, Ilkay Gundogan, we would have been stronger."
On whether City can catch the top two: "Tottenham are so strong. We saw again today that they are not going to drop points.
"Our performance away in that league was amazing this season. We dropped too many points at home.
"Look how strong Chelsea and Tottenham are at home. If you want to win the Premier League, you have to win at home to Middlesbrough and Southampton."
Southampton manager Claude Puel: "It's a disappointment because we can do better, we can create better opportunities.
"We did not have enough, we were not sufficient. It was not a good day for us, but congratulations to Manchester City."
- 2Cédric SoaresBooked at 41mins
- 8DavisBooked at 37mins
- 23HøjbjergBooked at 31mins
- 16Ward-ProwseSubstituted forLongat 60'minutesSubstituted forRodriguezat 82'minutes
- 20GabbiadiniSubstituted forBoufalat 60'minutes
- 42Y Touré
- 17De Bruyne
- 21SilvaSubstituted forZabaletaat 81'minutes
- 19SanéSubstituted forSterlingat 86'minutes
- 10AgüeroSubstituted forIheanachoat 89'minutes
- Neil Swarbrick
- Shots on Target
Second Half ends, Southampton 0, Manchester City 3.
Substitution, Manchester City. Kelechi Iheanacho replaces Sergio Agüero.
Substitution, Manchester City. Raheem Sterling replaces Leroy Sané.
Attempt blocked. Sofiane Boufal (Southampton) right footed shot from outside the box is blocked. Assisted by Dusan Tadic.
Foul by Yaya Touré (Manchester City).
Jay Rodriguez (Southampton) wins a free kick in the attacking half.
Substitution, Southampton. Jay Rodriguez replaces Shane Long.
Substitution, Manchester City. Pablo Zabaleta replaces David Silva.
Goal! Southampton 0, Manchester City 3. Sergio Agüero (Manchester City) header from the left side of the six yard box to the bottom left corner. Assisted by Kevin De Bruyne with a cross.
Goal! Southampton 0, Manchester City 2. Leroy Sané (Manchester City) left footed shot from the centre of the box to the centre of the goal. Assisted by Kevin De Bruyne following a fast break.
Corner, Southampton. Conceded by Nicolás Otamendi.
Corner, Southampton. Conceded by Nicolás Otamendi.
Attempt blocked. Maya Yoshida (Southampton) header from the centre of the box is blocked. Assisted by Dusan Tadic with a cross.
Foul by Kevin De Bruyne (Manchester City).
Ryan Bertrand (Southampton) wins a free kick on the left wing.
Attempt saved. Maya Yoshida (Southampton) header from the centre of the box is saved in the centre of the goal. Assisted by Dusan Tadic with a cross.
Corner, Southampton. Conceded by Jesús Navas.
Delay over. They are ready to continue.
Delay in match Jesús Navas (Manchester City) because of an injury.