On a sun-drenched afternoon on the South Coast, Raheem Sterling gave City an early lead, only for Southampton to equalise on the stroke of half time when Aymeric Laporte deflected the ball into his own net.
But three second-half goals sealed a fine victory. Kevin De Bruyne fired home a penalty after Gabriel Jesus was fouled inside the box, before substitutes Phil Foden and Riyad Mahrez produced outstanding quality to ensure safe passage into the last four of the FA Cup for the fifth time in six seasons.
City survived an early scare when Adam Armstrong timed his run superbly to latch on to Oriol Romeu’s slide-rule pass, but his first-time effort rebounded off the post with Zack Steffen beaten.
At that stage, Southampton were on top, but Raheem Sterling’s 12th-minute opener saw a new pattern emerge. Jack Stephens’ sloppy half-clearance was immediately pounced upon by Gabriel Jesus, who squared the ball for Sterling to tap City in front.
City’s passing game began to flourish, and we almost doubled our lead after 25 minutes. A drop of the shoulder from Joao Cancelo saw him buy a yard of space, before whipping a superb cross towards the near post. Ilkay Gundogan was there, but his volley rattled the upright.
But as the first half progressed, some of our play became sloppy and Southampton began to cause our backline problems with their direct, fast-paced counter-attacks. They levelled seconds before the break when Mohamed Elyounoussi’s cross was deflected into his own net by Aymeric Laporte after Steffen had come out of his goal and failed to claim the ball.
The timing of the goal may have been cruel, but Southampton deserved parity at half time after an industrious 45 minutes.
Jesus earned City a penalty on the hour when he was brought down by Mohammed Salisu on the edge of the box. Kevin De Bruyne stepped up and fired the ball past Fraser Forster, who went the right way but could not keep the Belgian’s spot kick out.
A moment of magic sealed it when Phil Foden struck a quite sensational effort past Forster from 20 yards to all-but confirm our semi-final berth.
And there was still time for a fourth - perhaps the best of the lot - when Mahrez struck his 22nd goal of the season. Cancelo's outrageous outside-of-the-boot pass was controlled by Gundogan on the chest before swivelling and finding Mahrez, who fired past Forster at the near post.
XI: Forster, Livramento, Stephens, Salisu, Walker-Peters, Romeu, Ward-Prowse (C), S Armstrong (Djenepo 83'), Elyounoussi, Long (Broja 63'), A Armstrong (Adams 63')
Unused subs: Caballero, Valery, Perraud, Diallo, Smallbone, Redmond
Starting XI: Steffen, Walker, Stones, Laporte (Ake 83'), Cancelo (Zinchenko 83'), Rodrigo (Fernandinho 83'), Gundogan (C), De Bruyne, Grealish (Foden 63'), Jesus (Mahrez 63'), Sterling
Unused subs: Carson, Bernardo
City show stomach for the fight
There can be little doubt this was, at times, a flawed performance from City, with our play too often stifled by misplaced passes and lapses in concentration.
But when a team are struggling to find their best form, they have to rely on other qualities, and City showed against Southampton we are capable of digging in to get a result.
Pep Guardiola will be pleased with the attitude and application of his players, but he will want to see our usual slick passing style return after the international break.
In addition to our fighting quality, Pep Guardiola was able to utilise his options to superb effect in order to get the win.
Phil Foden and Riyad Mahrez both started on the bench but produced quality when introduced.
It's unlikely Foden will ever hit a cleaner strike than the one he produced for City's third, and Mahrez's clever finish ended a fine passing move involving Joao Cancelo and Ilkay Gundogan.
Quality and class when needed.
Man of the match
Kevin De Bruyne.
Yet another inspirational display from the Belgian, who remains the most complete central-midfielder in world football.
Intelligence, vision and outstanding passing ability, he pulls the strings and conducts the City orchestra.
City have now scored four or more goals in a single match for the 80th time under Pep Guardiola in all competitions.
The next most such games by an English club in this time is Liverpool’s 58.
"We started really well and then we forgot to play. We know it's so difficult because Southampton are one of the best organised teams. It is so difficult.
"The second half was much better. We showed more personality. They had a chance with Adams but our quality made the difference.
"It’s not a comfortable victory. They are a tough opponent and we know it. Now we go into international break and we are in three competitions.
"Every game is a final. We have a chance still to fight for the FA Cup."
What it means
City are into the last four of the FA Cup for the fifth time in six seasons, where we will face Liverpool.
It means we remain in contention for three major trophies with two months of the season remaining.
We go into the final international break of the campaign one point clear at the top of the Premier League table, with our place in the quarter-final of the Champions League and last four of the FA Cup secured.
Pep Guardiola will be hoping his players return from international duty injury-free and ready to fight on three fronts in what will be a fascinating final period of the season.
A break from domestic football!
The international game takes centre stage for the next fortnight but once that is concluded, it’s a non-stop fixture list for City until the season’s end.
Our next assignment a trip to Burnley in the Premier League on Saturday 2 April, and three days later we host Atletico Madrid in the first leg of our Champions League last-16 tie.
Strap in and get prepared for some nerve-shredding moments.
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