Novak Djokovic advanced to the semi-finals of the ATP Tour Finals with a 100 percent record as the world number one defeated Czech fifth seed Tomas Berdych 6-2, 7-6 (8/6) at London's O2 Arena on Friday.
Djokovic had already defeated Andy Murray and Jo-Wilfried Tsonga in his previous Group A matches and the Serb knew he needed only to win one set against Berdych to be sure of qualifying.
The 25-year-old achieved that goal in just over half an hour, but he refused to take it easy after that and secured the victory which guaranteed first place in the group and potentially an easier route to the final.
In the process, Djokovic also secured his 73rd match win of 2012, moving him level with David Ferrer as the year's two most successful players on the Tour.
Berdych's second loss of the tournament means he is eliminated, while US Open champion Murray can seal his place in the last four by taking one set from his match against Tsonga later on Friday.
"I didn't want to think about scenarios or calculations. I leave that to other people and just try to do my job and win on the court," Djokovic said.
"I played a really good match but I thought he served better towards the end of the second set. I was fortunate to come back and win in straight sets."
Djokovic had won 10 of his previous 11 encounters with Berdych, a dominant run which included victories over the Czech in the Tour Finals for the last two years.
The Serb, who won the Tour Finals in 2008 in Shanghai, was quick to take command again, breaking for a 2-1 lead when Berdych netted on the fourth break-point of the game.
Berdych had a chance to get back in the match when he earned his first break point on the Djokovic serve in the next game, but the Serb snuffed out that glimmer of hope before pressing home his advantage.
Djokovic was dictating the tempo of the rallies and the unnerved Berdych, unable to cause much damage with his booming serve, surrendered a second break in the fifth game that effectively ended the first set.
With his last four place now secured, Djokovic looked like sprinting to victory when he broke to go 2-1 ahead in the second set, but a loose service game presented Berdych with an unexpected lifeline.
That gave renewed impetus to Berdych, who started to unload his groundstrokes with more freedom, and the set went to a tie-break.
The Czech looked certain to force a final set when he raced into a 6-3 lead in the breaker.
But Djokovic, who has had to cope with the stress of the sudden illness that struck his father Srdjan recently, once again showed tremendous resolve as he saved all three set points and then shattered with Berdych with a mini-break of his own to seal the win.