Dominant Manchester City powered into the FA Cup semi-finals after beating Southampton 4-1 at St Mary's Stadium on Sunday. Pep Guardiola’s side had failed to win either Premier League game against the Saints this season, but their emphatic victory kept them on course for a treble. Raheem Sterling had put the league leaders ahead in the 12th minute, only for Aymeric Laporte to level the scores with an own goal just before half-time. Kevin De Bruyne restored City's lead with 62nd-minute penalty after Mohammed Salisu brought down Gabriel Jesus. Phil Foden’s cracking finish made it three in the 75th minute, with Riyad Mahrez finishing off the victory three minutes later. "We started well, for the first 20-25 minutes but for the last 15 of the first half we forgot to play, knowing that this would be difficult because Southampton is one of the best, most organised teams we face all season," said Guardiola. "They push you with incredible intensity but the goal we conceded was a consequence of us forgetting to play. "The second half was much better, in personality and play. They had one chance for Che Adams, at 2-1, but the quality of our players up front made the difference. "It was not a comfortable victory but now we go into the international break, there are two months left in the season and we are in three competitions – semi-final of the FA Cup, quarter-final of the Champions League and top of the league. We know every game is a final and we knew it was important not to lose today." The home side nearly took an early lead on the south coast when Adam Armstrong was played in behind the City defence, but his slightly scuffed shot rolled back off the far post. It proved a costly miss as moments later, City took the lead with Sterling scoring his first goal since February 15. Jack Stephens failed to clear his lines, allowing Jesus to attack the loose ball and play in Sterling in the centre of the box, and the England forward made no mistake slotting home via a slight deflection off Tino Livramento. Fraser Forster made an instinctive diving save to deny Ilkay Gundogan from close range, just managing to tip the ball on to the post. Oriol Romeu had a chance to level the tie just before the half-time break, but his well-hit effort from the edge of the box was straight at City goalkeeper Zack Steffen. The hosts did equalise soon after when Mohamed Elyounoussi beat the offside trap and saw his effort deflected into his own net by Laporte. At the start of the second half Southampton worked well to break down City’s attacks and disrupt their playing style, while they had attempts of their own, including a James Ward-Prowse strike from range that Steffen was able to gather. With the tie delicately poised, the Saints' good work was undone when Salisu needlessly dived in on Jesus and referee Mike Dean pointed at the spot. De Bruyne dispatched the penalty, beating Forster who had dived the right way. Southampton came close to levelling the score for the second time, but Steffen was alert to save Adams’ effort after he was played in. City's strength in depth off the bench then took the game away from the hosts. First, Foden's struck a sweet left-footed strike from the edge of the box to make it 3-1, while Mahrez made it four with a low finish into the bottom corner. "I think the first 20 minutes and the last half an hour we did well," said De Bruyne. "In between we made too many stupid mistakes and even with their goal, we should have just played it out - there were 30 seconds to go until half-time. "We chose the wrong options and Southampton came back into the game. Not a lot was said at half-time but we had to play better and we did that. "But I think the reaction was really good - the second half, we dominated and we did much better. "We want to win every competition we enter, we have lost in a couple of FA Cup semi-finals but we are very happy and privileged we go again and hopefully we can win it this time."