- Arsenal ease into fifth round with comfortable win at St Mary's.
- Theo Walcott scores hat-trick in his first game of 2017.
- Danny Welbeck nets twice in his first appearance for the Gunners this season.
Full-time: Southampton 0-5 Arsenal
Two the two minutes of time added on here. Can Arsenal grab another?
Perez denied! He's released one-one-one with Lewis but the young goalkeeper makes himself big and makes an important block.
That's the match ball for Theo, then. From his own half, Perez plays a brilliant ball down the left for Sanchez. He draws in two Southampton defenders as he reaches the edge of the box and casually awaits for Walcott to arrive. When he does, the pass to his feet is perfect and he coolly slots home for his third.
Goal! Southampton 0-5 Arsenal (Theo Walcott, 84)
15 minutes left and St Mary's is starting to empty out. This match as a contest ended a while ago.
Here's Arsenal's third change, the impressive Reine-Adelaide makes way for Alex Iwobi.
Another fine goal from Arsenal and Southampton are done here. Oxlade-Chamberlain is again involved, picking out Sanchez who jinks his way down the byline before arrowing a pinpoint cross into Walcott who drives home into the far corner. Easy.
Goal! Southampton 0-4 Arsenal (Theo Walcott (68)
And here comes Alexis Sanchez, he comes on for Welbeck who has enjoyed an outstanding return tonight.
Here are two changes for Southampton, Nathan Redmond and Dusan Tadic come on with Shane Long and Lloyd Isgrove making way.
Alexis Sanchez is getting ready to come on now. You need that when you're three down.
Oxlade-Chamberlain is spraying passes around the pitch like a veteran deep lying playing maker this evening. This time he picks out Walcott but he loses control of the ball as he breaks into the box.
Perez holds the ball up in the box and waits for Bellerin to arrive and strike towards goal, but his effort is straight at the Southampton goalkeeper.
And we are back underway for the second half.
Half-time: Southampton 0-3 Arsenal
Ospina comes leaping out of goal to claim a Southampton cross but the Colombian is left in a heap after crashing into Shane Long.
Brilliant from Arsenal. They ping the ball around brilliantly as they advance into the final third with the Perez and Welbeck again combining neatly on the edge of the box. The Spaniard's ball finds Welbeck who opts to slide the ball across goal from a tight angle for Walcott, who taps home with Sam McQueen nowhere to be seen.
Goal! Southampton 0-3 Arsenal (Theo Walcott, 35)
Højbjerg whips one over the wall but it flies just wide of the post.
Josh Sims looks to be Southampton's best chance of pulling something back here. He harries Holding and wins the ball back 25 yards out from his own goal with Saints eventually winning a free kick as a result of his hard work.
Ospina was almost caught out a moment ago, but he's started to make up for it with a decent save to deny Shane Long. Martina picks out his striker with a brilliant ball curled down the right channel, with the Ireland international smashing his effort towards the near post only to be denied by the Arsenal 'keeper.
Brilliant from Danny Welbeck. Oxlade-Chamberlain picks out his run with a superb 40-yard pass, floating it over Gardos' head and right out the outstretched boot his his teammate. Welbeck keeps his cool and slots it under the onrushing Lewis; his second of the game.
Goal! Southampton 0-2 Arsenal (Danny Welbeck, 21)