It's all gone wrong for Chelsea. They started the second half much better than they finished the first, getting a bit of possession and hitting a couple of shots on target, but they've been undone by Ezequiel Lavezzi and their own errors. Napoli now lead 3-1 in the second half, and Lavezzi has a brace.
On a long ball over the top, David Luiz tried to control the ball and beat Edinson Cavani, but failed to do so. Luiz probably could have just put the ball out for a throw, but instead his error gave Cavani the chance to close him down. Luiz attempted a simple clearance the second time around, but struck Cavani with the ball.
Petr Cech had come out to deal with the ball, which was also a poor decision. Cavani got the ball under control and hit a pass across the goal to Lavezzi, who found himself facing an empty net waiting for the finish.
Sadly, this is what David Luiz will be remembered for on the day and on the season. Just a couple of minutes earlier, he made an incredible tackle on Lavezzi and moved the ball up the pitch to start an attack, but his errors have overshadowed his great plays once again.
For more on the Blues, head over to Chelsea FC blog We Ain't Got No History.