Defending champion Novak Djokovic survived a rocky third set to defeat American qualifier Denis Kudla to reach the last 16 at Wimbledon for the 13th time on Friday.

The world number one triumphed over 114-ranked Kudla 6-4, 6-3, 7-6 (9/7) to book a place in the fourth round of a Grand Slam for the 55th time.

Djokovic, chasing a record-equalling 20th major, cruised through the first two sets but then had to fight back from 1-4 down and also 1/4 in the tiebreaker before he recorded a 75th win at the All England Club.

"It's the trademark of every pro athlete that you never give up," said Djokovic who is halfway to becoming only the third man in history -- and first since Rod Laver in 1969 -- to complete the calendar Slam.

"I am always trying to give my maximum out there especially when playing one of biggest tournaments.

"When I was a little kid, I dreamed of winning Wimbledon."

Djokovic hailed his family roots for his on-court passion, which was evidence on Court One on Friday, as well as the struggles in growing up in Serbia in the 1990s (during the Balkans conflict).

"Part of it is genes. We grew up in difficult times for my country and failure was never an option," he said.

"We had to find basic ways to survive, that strengthened my character.

"Also my upbringing in the mountains I spent a lot of time with wolves -- this is wolf energy. I'm not kidding."

Six-time champion Djokovic next takes on 17th seeded Christian Garin of Chile.