Southampton got their promotion push firmly back on track as the Clarets' own top-six aspirations were given a reality check on the south coast.
A superb run of eight wins in 12 games since the end of November had allowed Burnley to flirt with the play-off places.
And their prospects of a late push have not been derailed by only a second away defeat in seven games.
But the manner of their loss will have confirmed to manager Eddie Howe that he still has a bit to do with his evolving side which was sunk by two goals before half time.
Adam Lallana's header and a Ben Mee own-goal got the Saints marching on again as they prepared for their mid-week summit meeting with Championship leaders West Ham.
At the same time the Clarets take on Barnsley at Turf Moor and Howe will be looking for a response to an off-the-pace performance devoid of the purpose and potency that had undermined their surge up the table since the end of November.
Adam Lallana puts the Clarets ahead
Southampton's imperious home form had taken a bit of a hit in recent weeks with no win since their year-long unbeaten record at the St Mary's had gone at the turn of the year.
But the Saints didn't start like a team with home sickness as they quickly had Burnley on the back foot.
It took a superb piece of defending from Kieran Trippier to deny Billy Sharp the chance to make his home debut with a goal as he latched onto an excellent pass from former Clarets' loanee Jack Cork.
But just two minutes later Burnley were undone as the Saints went in front, Lallana heading in Frazer Richardson's perfectly floated right-wing cross.
It could have quickly got worse for Howe's men as Danny Fox almost punished his former club, beating Trippier to pull the ball back for Rickie Lambert to bring a fine save out of Lee Grant.
Ex-Claret Jack Cork takes on Ross Wallace
From the resulting corner Dean Marney headed off the line from the dangerous Lambert and it was 24 minutes before the Clarets mustered an effort in response, the re-called Keith Treacy connecting well with a long-range volley but never really worrying Kelvin Davies.
That signalled an improved spell from the visitors but their task was made even harder when Southampton went 2-0 up with just over half an hour gone.
Sharp was always a threat in tandem with Lambert and having tested the impressive Grant with one effort, the January signing got in again from a Lambert assist and as Mee came across to cover, forced the Clarets' defender to divert the ball past Grant and into his own net.
If Burnley thought their luck was out then, they were further frustrated five minutes before the break when Jay Rodriguez - and a perplexed Howe - thought he should have had a penalty when pulled back by Jos Hooiveld, only for the decision to go against the Clarets' striker.
Burnley try to force an opening
But a two-goal margin was still a fair reflection and Howe responded by making two changes at the break with Josh McQuoid and Marvin Bartley coming on for Treacy and Dean Marney as the Clarets' boss tried to spark an improvement.
The result was the Clarets' best period of the game in the opening stages of the second half as they forced Southampton back for a sustained spell for the first time.
With Trippier getting further forward the ball was delivered into the box more often but invariably it was more in hope than expectation and only a semblance of a chance for McQuoid, which he couldn't poke past Davies, threatened to worry the home side.
The Saints still hadn't quite killed the game off, though, and they passed up two further chances with 25 minutes to go.
A mis-placed pass from McQuoid allowed Lambert and Cork to tee up Lallana for a close-range effort which hit Grant before Cork and Lambert combined again for David Connolly to steer an effort just wide with his first touch after coming off the bench.
Chairman Barry Kilby supports the Clarets with wife Sonya
His second had the ball in net, but this time from an off-side position as he followed up another effort from the rampant Lambert which had Grant scrambling to save on a day the keeper had needed to be arguably the Clarets' best player.
Burnley: Grant, Trippier, Mee (Hines 75), Duff, Edgar, Marney (Bartley ht), McCann, Wallace, Rodriguez, Austin, Treacy (McQuoid ht). Subs: Easton, Jensen.
Southampton: Davies, Richardson, Fox, Hooiveld, Schneiderlin, Fonte, Cork, Do Prado (Hammond 78), Sharp (Connolly 64), Lambert (Lee 90), Lallaana. Subs: Martin, Puncheon.
Referee: Trevor Kettle
Attendance: 24,099 (1,040 Burnley)
Not their day