Roger Federer made it back-to-back wins at the ATP World Tour Finals by beating world number one Novak Djokovic 7-5 6-2 at the O2 Arena.
Mistakes at vital stages ended Djokovic's winning run at 23 matches as Federer moved into pole position in the group.
Unforced errors were a rarity for much of the opening set as the two players put on an impressive show full of long rallies and unstoppable winners.
After Federer had saved break point in the opening game of the match, both men looked composed on serve as the games quickly raced by.
Federer missed one opportunity at set point in the 12th game when he found the net with a forehand, but he refused to let another chance escape him as a stunning drop shot left Djokovic helpless.
It soon became worse for Djokovic when Federer secured a break early in the second set, but the world number one responded impressively to immediately break back.
Errors crept back into Djokovic's game at a crucial stage, and Federer was in the mood to capitalise as he used a break point to take a 4-2 lead with a backhand winner.
The pressure was back on Djokovic again on his next service game, and despite saving one match point, he was unable to hold off Federer, who finished the match off to move to the brink of reaching the knockout stage.
