Chelsea have moved five points clear at the top of the Premier League table with a 2-0 win over rivals Arsenal at Stamford Bridge.
Alexis Sanchez was keen to make an early impression on the game as he sent a speculative 30-yard effort towards goal, but it flew harmlessly wide of Thibaut Courtois's right-hand post.
Sanchez then collided heavily with the Chelsea shot-stopper as Arsenal looked to break forward, which eventually led to the Belgian being replaced by Petr Cech.
Both sides were fully committed throughout the first half, and tempers flared when Gary Cahill's robust tackle on Sanchez caused Arsene Wenger and Jose Mourinho to confront each other on the touchline.
Chelsea then made the breakthrough on 28 minutes as Eden Hazard was brought down by Laurent Koscielny inside the box before slotting the resulting penalty confidently past Wojciech Szczesny.
Jack Wilshere should have got Arsenal level moments later when he was sent through on goal, but a poor first touch allowed Cech to come off his line and gather the ball as Chelsea went in 1-0 up at the break.
The visitors started the second half in positive fashion, with Santi Cazorla shooting narrowly wide of the post after a spell of pressure.
Despite Arsenal's early dominance, Chelsea were soon back in the ascendancy thanks to a chance for Hazard that saw the winger's shot come off Mathieu Flamini and almost find its way past Szczesny.
The Gunners, who were stifled for large periods of the game, were wanting a penalty midway through the half when Cesc Fabregas looked to have handled inside his own area, but referee Martin Atkinson waved away the appeals.
Chelsea then made sure of the points on 78 minutes as the unusually-quiet Diego Costa latched onto Fabregas's incisive pass before lifting the ball over Szczesny and into the net.
Arsenal had a late chance to reduce the deficit through substitute Lukas Podolski, only for a combination of Cech and Cahill to snuff out the danger.