Right then, that's all from us for this evening. 

If you're just joining in, feel free to catch up on things below, and you can head over here for Phil McNulty's match report.

Until the next time...

Image source, Getty Images

A hat-trick for Theo Walcott, two goals and an assist for Danny Welbeck on his return after eight months out injured. Saturday afternoon couldn't have gone much better for Arsenal. Steve Bould could get used to this.    

The Gunners go through to the FA Cup last 16. Join us on Monday evening for the draw.

Sunday? How about two games on the telly?

Millwall v Watford (12:00 GMT) BBC One from 11:50.

Manchester United v Wigan Athletic (16:00) BBC One from 15:30. 

Sunday night highlights BBC One from 22:30 .

Southampton

Southampton boss Claude Puel: "I am responsible for the defeat. If I had to do other team at the start I would make the same because it is a difficult moment for us with all these games. We had nine players not available and I had to protect some players. It is not possible to play every three days with the same players and with some players with injuries.

"It is important for us to think other things. It was a good lesson, they are a great team. We started the game without good experience and were nervous. It was better in the final 10 minutes of the first half and in the second half it was interesting, it was a good reaction in the collective."

Our chief football writer Phil McNulty's giving some of his post-match thoughts. 

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Arsenal

More from Arsenal boss Arsene Wenger: "We were very dynamic, explosive and overall we had a good consistent performance over 90 minutes and everybody played well.

"Welbeck has been out for such a long time, I didn't expect him to score straight away and it shows the desire is there. 

"People say I make changes but I bring in Walcott, Welbeck and Perez, all top quality players. After that I try to find the best balance for the team."

Arsenal

Arsenal manager Arsene Wenger, on BT Sport: "I think it was good to watch because we had a good game and were very dangerous. We were in control, very explosive. 

"Danny Welbeck was very sharp because he has been working very hard. He comes back from a long way out and has gone through some very difficult moments mentally. But his resilience was absolutely marvellous and he was rewarded tonight, so we are happy." 

Experience of being up in the stands?

"You miss something. I have spent so much time on the bench that physically it is difficult to be far away, but the most important thing is Arsenal to win."

Image source, Reuters

Arsenal

Arsenal forward Danny Welbeck, on BT Sport: "I've had experience of coming back from injury before so you kind of know what to expect. But it was good to finally be back on the pitch. It's been a horrible few months with the injury but to be back out there doing what I love and scoring goals, is great." 

Arsenal

Arsenal forward Theo Walcott on BT Sport: "Southampton tend to be our bogey side but from the word go we were ready. We came out of the blocks running and Danny Welbeck came back with a bang. We created a lot of chances and it was nice to have the clean sheet.

"Southampton will always be in my heart I have some great memories here, they are a strong team and I will cheer them on in the EFL Cup final."

Image source, Reuters

Theo Walcott has had a night to remember against his former club. 

Big Gray: Stevie Bould's blue and yellow army!

Who needs Arsene Wenger?

Danny Mills
Ex-England defender on Radio 5 live

Theo Walcott and Danny Welbeck both played very, very well.

The guys are talking about changes and Southampton made too many. Their young players looked in awe of the Arsenal players.

It was a very comprehensive, easy win.

It ended with a Walcott hat-trick, but while we get that one wrapped up, check out Theo's finish for Arsenal's fourth.

Karan Singh Pannu: Can someone just speak to Arsenal membership team and give Wenger a seat in Clock end upper for the rest of the season?

Into two minutes added time we go.

Steve Bould's debut as Arsene Wenger's step-in hasn't gone too badly at all. Three matches of the Frenchman's ban left. Three more wins?

Lucas Perez, impressive with some great passing and inventive play, has a chance for a goal of his own as he bears down on the keeper, played clean through...

But Harry Lewis denies him, rushing off his line to block. Again, a fantastic pass from Alex Oxlade-Chamberlain to find the Spanish forward.

Image source, Reuters

Looks like Arsene Wenger's seen enough too. He's beating the rush for the bovril bar, accompanied by a gaggle of stewards on the way down to what will be a very happy Arsenal dressing room. 

Two for Danny Welbeck on his return, a hat-trick for Theo Walcott. A place in the last 16 awaits.

Image source, PA

Ojelabi Tosin: Southampton knock out Arsenal from the League Cup and reach the final. If Arsenal knock out Southampton will they reach the final?  

Meer Shah: 2 for Welbs, 3 for Walcott. Not a bad day at the office. Picking up where Giroud left off. Still more goals to come from them 

Phil McNulty
BBC Sport chief football writer at St. Mary's

Lots of Southampton fans have seen enough and have started to make their way to the exits. They have seen their team utterly thrashed tonight.

Arsenal have simply strolled to victory and the Saints fans don't seem too upset by it - it has been a momentous week and they still have that EFL Cup Final against Manchester United to look forward to.