Roger Federer insists he will not ease up when he takes on Juan Martin Del Potro in his final Group B match at the ATP World Tour Finals.
The Swiss ace has already qualified for the semi-finals of the London tournament at the 02 Arena courtesy of a straight-sets victory over David Ferrer after previously beating Janko Tipsarevic.
Federer has now claimed 14 straight successes over the Spaniard and the 31-year-old modern great and will look to remain unbeaten against Del Potro on Saturday.
"I've been in this situation before. You want to keep a clean sheet going into the semis," he told Sky Sports.
"You don't want to lose your last match of the round robin. As ever I'm going to try my very best and hopefully I can play a good match against Juan Martin."
Despite the 6-4 7-6 win over Ferrer, who won the Paris Masters on Sunday, Federer said he was thoroughly tested.
"I'm extremely happy. It was a tough match," he continued. "I'm thrilled and relieved that I've qualified.
"David's obviously been on a great run, winning in Paris was so deserving for him.
"He puts in so much effort. It was a long match for two sets. I played a great match."