Steve Claridge
Ex-Leicester striker on BBC Radio 5 live

Chelsea fully deserved the win. They negated a very good side in Southampton.

There must be something in the air because Costa is hugging everyone - not just his own team. It just shows the togetherness of those players and the job they've done. It was a really, really good team performance. You have to take the context into account as well, Southampton are a very very good side. 

If you wrote the script beforehand, Chelsea would say that's exactly what they wanted to happen. 

Image source, Reuters

So Southampton's recent run comes to an end. That's their first Premier League defeat in six matches. They stay ninth.

Alistair Bruce-Ball
on BBC Radio 5 Live

I don’t think Courtois has made a save of note. That shows how good Chelsea’s defence have been because it’s not like Southampton are a bad side. 

Fine time. Chelsea's players are full of smiles (even Diego Costa), their manager pulling a strange gurning face that indicates he is happy.

The Blues are back up to fourth - just one point behind leaders Manchester City.

Image source, @Chelsea

Chelsea win a free-kick just outside the Saints box, close to the left byeline. They have no intention of trying to get a third on this occasion. Eden Hazard goes backwards and within 10 seconds it is at Thibaut Courtois' feet.

Chelsea still fancy a third. Nemanja Matic's cheeky backheel finds Willian, who drills wide.

The home stands are emptying quicker than a nightclub when the lights come on. Jose Fonte shanks a pass out of play - and that sums Southampton's afternoon. Three minutes of stoppage time.

Chelsea waste a few more seconds with a switch. Goalscorer Diego Costa is removed - again to a standing ovation from the away fans - with Michy Batshuayi given a late opportunity.

Image source, Getty Images

'Ole!' football from the visitors now. The away end greets every pass with a huge cheer as Chelsea knock the ball around in midfield.

Image source, Getty Images

Chelsea running down the clock with another change. Off goes Victor Moses - to a well deserved standing ovation - on comes the more defensively-minded Branislav Ivanovic. Chelsea are bolting up the door.

Steve Claridge
Ex-Leicester striker on BBC Radio 5 live

You almost get the feeling that it’s going to be who defends best that wins the Premier League - they can all score goals.

Goal! No. Charlie Austin tucks in a cross from the left - the flag is raised. The Southampton striker just went a fraction too early.

Image source, Reuters

I want whatever Victor Moses has been drinking in recent weeks. He's been revitalised. The newly-discovered wing-back dances in from the right, launching a fierce drive that Fraser Forster beats away unconvincingly.

Image source, PA

This has turned into a keep ball exercise for Chelsea now. Running down the clock.

Has Antonio Conte's 3-4-3 system transformed Chelsea's title chances? A win today will take them within a point of top-of-the-table Manchester City.  

Dave Local: Chelsea look very focused and solid at the back, something they totally lacked last season.

Jose Akinlabi: Chelsea are now so brilliant in defence and sting on the counter with Conte's magical 3-4-3.

Aaron Trowse: David Luiz since the system change to 3-4-3 has been an absolute revelation. Long may it continue.

Have your say at #bbcfootball on Twitter.

If Saints are going to set up a grandstand finish then they'd better get a move on. No sign of one yet.

And Chelsea decide to make a change too. Pedro's day is done, Willian comes on.

Double trouble for Chelsea? Saints hope so. They throw on Pierre-Emile Hojbjerg and Sam McQueen for Ryan Bertrand and Dusan Tadic.

That set-piece is dealt with comfortably by the visitors. And there's plenty of activity on the touchline...