Chelsea showed no mercy in extending their Premier League lead to six points on Saturday, brushing aside promoted Norwich City 4-0 while second-placed Everton were held to a 0-0 draw at Blackburn Rovers.

Manchester United remained nine points behind Chelsea in fourth place after a 5-2 victory against Crystal Palace at Old Trafford in a lively evening kickoff.

First-half goals from Damien Duff, Frank Lampard and Arjen Robben and a superb Didier Drogba header late on handed Jose Mourinho's Chelsea a comfortable win at Stamford Bridge.

Chelsea, who have hit four goals in six of their last nine league games, hold an eight-point advantage over champions Arsenal who can cut that deficit and go second if they overcome Portsmouth at Fratton Park on Sunday.

Chelsea served up another four-goal show for their fans in defeating a Norwich side who have won only two matches since their return to the top flight.

"I think we deserved the victory, no doubt," Mourinho told Sky Sports. "I cannot remember a difficult situation for (goalkeeper) Peter Cech but to be fair, in the first half, they were better than us.

"Norwich had some control of the game. It was difficult for us but our front players are very dangerous -- on the counter-attack they are very difficult to stop.

"The second half we had full control of the game."

Duff was gifted his seventh goal of the season after 10 minutes from a wayward pass.

SLACK DEFENDING

More slack defending led to Dutch winger Robben squaring for Lampard to crash an unstoppable shot into the roof of the net for his 50th Premier League goal and Robben hit the third just before halftime. Substitute Drogba added the gloss with a fine header from Duff's corner seven minutes from time.

Everton remained in an automatic Champions League place but missed the chance to notch their 12th victory against a resilient Blackburn side who edged out of the relegation zone with a point at Ewood Park.

Blackburn, without a home league win since September, could have taken all three in stoppage time but Brett Emerton's deflected shot struck the woodwork.

Everton boss David Moyes said his side were not at their best. "We were slow coming out of the blocks and never really recovered. But you can't take this point (from the draw) in isolation. We've taken seven points out of nine in our last three games."

Wayne Rooney missed a penalty for Manchester United against Crystal Palace but it did not prove costly as two goals from Paul Scholes helped Alex Ferguson's side to victory.

Scholes opened the scoring after 22 minutes and Alan Smith's header made it 2-1 at halftime after Danny Granville had jabbed Palace level on 27 minutes.

An explosive start to the second half produced three goals in four minutes. Joonas Kolkka headed Palace level again before an own goal by Emmerson Boyce and a second for the razor-sharp Scholes restored order. John O'Shea completed the victory in the final minute.

Fifth-placed Middlesbrough completed a satisfactory week by following up Wednesday's UEFA Cup win over Partizan Belgrade with a 3-0 victory over Aston Villa at the Riverside.

Villa had plenty of possession but goals from Jimmy Floyd Hasselbaink, Joseph-Desire Job and Michael Reiziger wrapped up the points.

DEFOE HAT-TRICK

Tottenham Hotspur striker Jermain Defoe collected his first Premier League hat-trick as the Londoners climbed to seventh with a 5-1 demolition of hapless Southampton.

The England striker scored twice in the first half with Frederic Kanoute also on target to put Spurs on course for a fourth consecutive league win -- their best run since 1995.

Defoe completed his hat-trick after Peter Crouch gave Saints a lifeline and substitute Robbie Keane added a fifth to leave Harry Redknapp's side stuck in the bottom three.