Defending champion Novak Djokovic has won under the lights at Wimbledon, beating American Ryan Harrison 6-4 6-4 6-4 in the final match of the day.

With the schedule delayed because of afternoon rain, Djokovic and Harrison played under the retractable roof on Centre Court and finished their second-round match at 9.52pm on Wednesday (0652 AEST on Thursday).

The top-seeded Djokovic lost only four points on his second serve and saved all six break points he faced.

He has won three of the past four Grand Slam titles but was beaten this month in the French Open final by Rafael Nadal.

The Serb next tackles either Czech 28th seed Radek Stepanek or German Benjamin Becker for a place in the last 16.