Novak Djokovic may not have been at his best, but the Wimbledon top seed still managed to beat Tommy Haas in straight sets and secure a place in the quarter-finals.

Having seen fellow world No.1 Serena Williams felled earlier on Centre Court, the 26-year-old Serbian ensured he would not follow suit on the day in the tennis year commonly known as 'Manic Monday'.

Djokovic won his toughest clash of the tournament 6-1, 6-4, 7-6 (7/4) in two hours and 12 minutes as 35-year-old Haas provided the "big challenge" he had predicted.

Despite almost being pushed to a fourth set by the veteran, the world No.1 was chipper in his post-match TV interview.

"It was always going to be tough," he said. "I had a bad record against him.

"I lost twice in 2009 against him. He is a grass court specialist, he has a great variety in his game, so it was a tough challenge for me but I played really well.

"I knew he would improve. He missed a lot of easy shots in the first.

"I had to work and I was serving well, returning exceptionally good in important moments."

Next up for Djokovic is another tough-looking tie, with Tomas Berdych standing in his way of a semi-final berth.

"I lost to him when we played in 2010 so I am playing against players I have a bad record against," he said.

"I think I am playing really, really good tennis at this moment, better than in 2011 when I won it, so I feel confident."