Leaders Chelsea tightened their grip on the Premier League's top spot with a commanding victory over West Ham.

The Blues had already come close through Oscar and Gary Cahill when John Terry turned in Diego Costa's header from close range.

After a tame first half, West Ham offered more in the second, but their hopes were snuffed out by Costa's drilled finish just after the hour.

Morgan Amalfitano hit the post late on but Chelsea racked up 28 shots at goal.

Chelsea are set to finish 2014 at the top of the table - and the quality of their performance suggested they may well still be there in May.

Their manager Jose Mourinho accused West Ham of playing "19th century football" after the teams' goalless draw at Stamford Bridge in January, but this Blues side, with the attacking threat Costa and Cesc Fabregas, never looked like being denied.

The visitors' style has taken a quantum leap forward since - with 29 goals in their first 17 league games this season compared to 14 over the same period in 2013-14 - but it was clear as soon as the team sheets were published that Sam Allardyce intended a defensive performance similar to 11 months ago.

The West Ham manager dropped Alex Song and Diafra Sakho to the bench ahead of Sunday's meeting with Arsenal and told television before kick-off that "we have to stop Chelsea - it's as simple as that".

His ambitions were almost undermined by Carl Jenkinson's lapse inside the first five minutes.

The right-back, on loan from Arsenal, allowed Oscar to dart in behind him and was relieved to see the Brazilian blaze over from six yards out after latching onto Willian's floated ball in.

But it was only a temporary reprieve.

Gary Cahill thumped a shot straight at Adrian and the seemingly inevitable Chelsea opener arrived after Eden Hazard almost wriggled his way in on goal.

James Collins' last-ditch tackle had denied the Belgian on that occasion, but from the resulting corner the defender lost Terry, who was free to poke in as Costa flicked on.

The Blues did not let up and Costa punted over when well placed before Branislav Ivanovic appealed in vain for a penalty as he went down under Andy Carroll's challenge.

For West Ham, with only 27% of possession, Chelsea's slim scoreboard advantage was the only positive to take from the first half.

The away side briefly flickered into life after the break and Terry had to be alert to cover across and block Valencia's route to goal.

Sakho and Song were introduced for the Hammers but, just as a few concerns could be felt around Stamford Bridge, Costa's dead-eyed finish ensured the home fans could enjoy the final half hour in comfort.

The Spain international's dummy took Tomkins, Winston Reid and Carl Jenkinson out of the game before his fierce low drive did likewise for goalkeeper Adrian.

A late cameo for Didier Drogba was applauded warmly and West Ham were denied a late mood-killing consolation as Amalfitano's flick hit the woodwork after a neat run took him past Terry and Cahill.