Novak Djokovic: Through in five sets

Novak Djokovic has said he would apologise to a Wimbledon ball girl after his outburst during his fourth-round win over Kevin Anderson.

The defending champion appeared to aggressively shout "towel" at the startled youngster when facing the South African in his fourth-round match on Court One .

Djokovic won through 6-7 (6-8) 6-7 (6-8) 6-1 6-4 7-5, resuming on Tuesday after fading light had brought the match to an overnight halt after four sets.

When asked about the incident involving the ball girl, which came after he planted a loose forehand into the net to end a 20-shot rally, Djokovic said: "I'm sorry. There was nothing towards her. Maybe she was just afraid of my screaming there.

"Sometimes it's just good to scream and let it all out, because that's the way I work. I was pretty close to her. I'm definitely going to try to apologise to her if I did something wrong."

Djokovic's safe progress to the quarter-finals came on the 30th anniversary of coach Boris Becker's first Wimbledon triumph as a 17-year-old.

"I didn't know it was today. But he's going to have a glass of wine, I'll have a glass of water, and we will celebrate this nice milestone," Djokovic said.

Becker said of Djokovic's performance: "I think that's a message to the locker room that whoever said he wasn't ready before, well he's ready now."

Novak Djokovic is 'ready now' according to his coach, Boris Becker

The 28-year-old world No 1 will face US Open champion Marin Cilic on Wednesday in the quarter-finals. They have played 12 times previously, and Djokovic has yet to taste defeat.

The Serb said of his Croatian rival: "He had an exceptional season last year, the best of his life. He played very well at the Grand Slams, and of course won the US Open. That's the crown of his career.

"I remember him mentioning earlier this year that he wants to focus mostly on Wimbledon, grass. That's where he feels like he has a best chance besides the US Open."

Djokovic: Said victory over Kevin Anderson was one of the most difficult of his career

Djokovic labelled his tussle with Anderson "one of the most difficult in my Wimbledon career" and said the 29-year-old played "exceptionally well".

"Obviously the fifth set today was very frustrating, very tense," Djokovic said. "I didn't have basically any chances on his serve till the 11th game when he made two double faults and I made a couple of good returns from the forehand side. That was enough."

Anderson was beaten in straight sets by Andy Murray in the Queen's Club final last month and said it was "more comfortable" to tackle Djokovic on grass than the Scot, although he finds it hard to look beyond the pair as potential

champions.

Anderson: Believes Djokovic and Andy Murray are favourites to win Wimbledon

"I think I was more settled playing Novak than I was against Andy. I lost a couple of early breaks to Andy. He served well. I didn't have too many looks there," Anderson said.

"They're both playing good tennis. If they get to the final, it will obviously be a very exciting match.

"It will be really interesting to see what progresses. It would be really hard to pick outside of Andy and Novak. If I had to pick one, I would just be guessing. You could probably guess as well as I could."