WIMBLEDON, England - It's a sporting cliche, but an accurate one. The way an athlete responds when in trouble is a yardstick of his quality. Novak Djokovic, the No. 1-ranked player in men's tennis, responded well enough at Wimbledon to reach the quarterfinals of a Grand Slam tournament a 25th straight time.

In a match that began Monday and then after four sets was suspended because of darkness, Djokovic Tuesday completed a successful comeback, defeating Kevin Anderson, 6-7 (6), 6-7 (6), 6-1, 6-4, 7-5 on Court One.

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The 6-foot-8 Anderson, a South African who played at Illinois, had 40 aces, including three in the first game of the fifth set. But Djokovic, the defending champ and winner of eight majors overall, including this year's Australian Open, had the better overall game.

"Kevin served exceptionally well," Djokovic said. "I find this was one of the most difficult matches I've played at Wimbledon, maybe in my career. At times I was really helpless with my return."

But big servers don't get every ball in. Anderson, who's never been past the fourth round of a Slam event, made consecutive double faults in the 11th game of the final set on his way to losing the match.

"To come back and win in five definitely gives me great satisfaction and confidence for the next challenge," Djokovic said.

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That will be Wednesday against U.S. Open champ Marin Cilic, against whom Djokovic has a record of 12-0.