LONDON - Defending champion Novak Djokovic displayed his liking for Wimbledon's roof again with a late night second round victory over American upstart Ryan Harrison on Wednesday.

The world No.1 Serb was delayed getting on court for his second round match after steady light rain interrupted proceedings at the All England Club but he made sure of a rest day on Thursday by completing a routine 6-4 6-4 6-4.

He was not at his best throughout an entertaining contest but was pleased to avoid any real drama after fending off a mini-crisis in the middle of the second set when he trailed 0-40 on serve at 2-3 to the American.

Novak Djokovic of Serbia serves to Ryan Harrison of the US during their men's singles tennis match at the Wimbledon tennis championships in London June 27, 2012.[Photo/Agencies]

"It was great to be under the roof once again," Djokovic, who came through a late-night five-setter against Olivier Rochus in the first round two years ago, told reporters.

"I thought it was a very exciting match to be a part of as a player, and I thought the crowd enjoyed it as well."

Having re-established control against the world number 48, Djokovic was rock solid as he closed out victory well before the 11pm cut-off time for play.

He failed to convert his first match point when he netted a drive volley but he sealed victory with a service winner to set up a third-round match against 28th seed Radek Stepanek or German Benjamin Becker.

"It's hard to prepare for that because you play indoor match on the Centre Court maybe once every couple of years," he said.

"2010 was my only match under the roof aside from tonight's match. It is quite different.

"I think the lights were really good. The attendance was fantastic. The crowd enjoyed it. It was a spectacular match from a player's point of view. Sometimes it's good for a change to be under the roof. It makes it more interesting as well I think, if you go to the late hours."

The lights of Centre Court shine through the closed roof during the men's singles tennis match between Novak Djokovic of Serbia and Ryan Harrison of the US at the Wimbledon tennis championships in London June 27, 2012.[Photo/Agencies]