Two goals from James Beattie and second-half strikes from Marian Pahars and Chris Marsden saw Gordon Strachan's put some welcome daylight between them and the relegation zone.

Chelsea, billed as championship challengers after wins over Liverpool and Newcastle, led 2-1 at half-time through Jimmy Floyd Hasselbaink and Eidur Gudjohnsen but a woeful second-half show saw them slip to the shock result of New Year's Day.

But while it was certainly a case of New Year, same old inconsistent Chelsea, it was not all about the expensively assembled home side. Strachan had promised the Saints would come and attack and they did that superbly on the counter.

The whiff of a shock was in the ice-cold west London air as early as the seventh minute when Beattie started the scoring spree with a masterful free-kick, bent over the wall and into the top right-hand corner from 35 yards after John Terry had bundled Pahars over.

Before today only Charlton had taken three points away from Stamford Bridge and after Hasselbaink had rifled just wide, his glancing header was only parried by Paul Jones and the in-form Eidur Gudjohnsen smashed home the rebound to make it 1-1.

Hasselbaink then lobbed over and Sam Dalla Bona drove wide as Chelsea threatened to reproduce the sort of display that had knocked Newcastle off the Premiership summit and thrust Claudio Ranieri's men into the championship melting pot.

Their odds must have been shortened right on half-time as Gudjohnsen sent his Dutch strike partner through and Hasselbaink slotted home his 15th of the season.

But whatever Strachan said to his side during the break worked wonders, although they were helped by a disjointed midfield display from the home side, who were outfought and out thought, with Paul Williams mopping up at the back and Pahars rampant on the break.

It was Williams who created the second equaliser on 55 minutes as he drove a superb 40-yard diagonal pass into the path of Pahars, who held off the otherwise excellent William Gallas to slide a precise finish inside Carlo Cudicini's far post.

Eight minutes later and the New Year Blues were all Chelsea's as a Paul Telfer corner skimmed of the head of Frank Lampard and fell perfectly for Marsden to slam a powerful header home and put his side in front for the first time.

The balding midfielder almost glanced in a carbon copy on 70 minutes only to see it go just wide, but with the Saints growing in stature and Chelsea shrinking by the minute, it was really no surprise when the fourth went in just two minutes later.