Chelsea took a giant step towards pipping Manchester United for second place in the Barclaycard Premiership behind Champions Arsenal - but only after being spurred into life by a huge slice of luck against the battling Saints.

Claudio Ranieri's men struggled to break down Paul Sturrock's defensively-minded team until the 59th minute when England youth captain Martin Cranie - making his Premiership debut thanks to the club's injury crisis - headed an own goal.

That sparked a collapse by Southampton and Frank Lampard struck twice in the space of eight minutes before Glen Johnson came off the bench and completed the romp with a goal four minutes before the end.

With United surprisingly beaten at Blackburn, Chelsea go to Old Trafford next weekend with a four-point cushion over Sir Alex Ferguson's men.

Not only did Chelsea go into this game without a win in their last five games, they also had failed to score in their previous two matches at Stamford Bridge.

That was almost put right after 13 minutes when Cranie lost possession to Eidur Gudjohnsen just outside the area and he flashed a fierce drive inches wide of Antti Niemi's left post.

There was a nervous moment for Chelsea after 17 minutes when Saints won a free-kick 25 yards from goal, just left of centre.

James Beattie hit a low curling drive beyond the wall and Carlo Cudicini - back in goal after an 11-match absence with a hand injury - spilled the ball at the near post. Kevin Phillips tried to make it first to the rebound but was just beaten by Mario Melchiot.

Joe Cole was denied again after 28 minutes following a corner on the right. From Geremi's cross Robert Huth laid the ball off to him on the edge of the box and his rising shot was well tipped over by Niemi.

Higginbotham was lucky to escape conceding a penalty after 31 minutes following a rash tackle on Jimmy Floyd Hasselbaink.

The big defender caught the Dutch striker just inside the box, but referee Paul Durkin and his assistant got it wrong by awarding a free-kick just outside the area rather than the penalty it should have been.

Kenton was playing out of his skin and came to Southampton's rescue again after just 90 seconds of the restart.

Hasselbaink beat the offside trap and looked certain to score as he ran into the box, but Kenton made up ground to get in a brilliant block tackle.

The home fans were almost left completely silent after 58 minutes when Terry's header back towards goal fell short and Phillips tried to lob Cudicini, but the Italian was able to make the catch.

That proved something of a turning point as Chelsea enjoyed a huge slice of luck to take the lead after 59 minutes from an own goal.

Gronkjaer chipped in a near post corner from the right and Cranie knew little about it as he headed the ball past Niemi at the near post.

Chelsea almost let Southampton back into the game after 75 minutes but Cudicini came to the rescue with a point blank save to deny substitute Brett Ormerod.

It was another turning point as Chelsea broke away, Gudjohnsen saw his shot blocked and Lampard followed up to fire the ball home.

Saints crumbled in the final stages and Lampard helped himself to a second goal after 84 minutes.

This time Niemi blocked Hasselbaink's shot and the England midfielder followed up to stroke home the rebound.

It became a romp as Glen Johnson came off the bench and added a fourth after 86 minutes with his first touch after Gudjohnsen pulled the ball back from the right.

Having rediscovered their scoring touch, Chelsea must overturn a 3-1 deficit when Monaco arrive at Stamford Bridge for the Champions League semi-final, second leg, on Wednesday.

Teams

Chelsea Cudicini, Bridge, Terry, Huth, Melchiot, Cole (Veron 79), Lampard (Makelele 86), Geremi, Gronkjaer (Johnson 78), Hasselbaink, Gudjohnsen.

Subs Not Used: Ambrosio, Crespo.

Goals: Cranie 59 og, Lampard 75, 83, Johnson 85.

Southampton Niemi, Cranie (Fernandes 63), Lundekvam, Higginbotham, Telfer, Folly, Kenton (Hall 78), Anders Svensson (Ormerod 68), Prutton, Phillips, Beattie.

Subs Not Used: Blayney, Crainey.

Att: 41,321

Ref: P Durkin (Dorset).