John Terry believes Chelsea have heaped the pressure on title rivals Manchester City "to try to stay close" to the Premier League leaders.

Terry headed Chelsea into the lead against West Ham before Diego Costa sealed the Blues' 2-0 win, their ninth-straight league victory at Stamford Bridge this term.

Jose Mourinho's men edged into a six-point lead at the top of the table thanks to their early Boxing Day kick-off

Former England defender Terry stoked the title-race fires after his second goal in as many games, claiming the onus now lies with City to keep pace with Chelsea.

"I think we're playing well, and playing before teams it's a chance for us to go six points clear," said Terry.

"And the pressure's on them now to win, and to try to stay close to us.

"We're playing great now, everyone can see that, and if we continue to do that it's going to be tough.

"The title is the target for us, right from day one.

"We've got off to a good start, and if we continue our form it's going to be tough for anyone.

"We are playing great at the minute but that can change over two or three games, everyone's seen that.

"It's important we remain calm and keep doing what we're doing right now which is playing good at the moment.

"I see a hunger among the players that haven't won the league."

Spain hitman Costa fired his 13th goal in just 15 Premier League games since his big-money summer move from Atletico Madrid.

Chelsea manager Mourinho believes the Brazil-born striker is continuing to blossom in a new attacking set-up at Stamford Bridge.

"This is (Cesc) Fabregas football, this is (Eden) Hazard football, this is Willian football, this is Oscar football," said Mourinho.

"Diego is adapting to that because in Atletico he was a different kind of striker, but even Diego is adapting well to that football we are playing when we have possession of the ball.

"One more match to the end of the first run, and that's right (for us) to finish first.

"This is the football of the team that leads, and leads with all the credit they deserve.

"We are playing very, very well, so it's the football that can put the team as a leader and clearly as a title contender.

"But we've only finished the first lap and there's still plenty more to go."

West Ham boss Sam Allardyce admitted conceding goals from set-pieces "kills me" after Terry headed the opener from a corner.

"It kills me, because we do our markings every single week," said Allardyce.

"We are one of the best at defending this season and that's why we are where we are.

"But that is disappointing against a team as good as this, because you've got so much to worry about in general play.

"We switched off.

"Chelsea were the better team, but when you carve out those kinds of chances in the last 20 minutes you want to put one in and just see if they get nervous or not.