NEWPORT, R.I. (AP) -- Top seed and defending champion John Isner beat qualifier Sergei Bubka of the Ukraine 7-6 (3), 4-6, 6-3 in an opening round-match at the Hall of Fame Tennis Championships on Tuesday.

Isner, ranked 11th in the world entering the week and a U.S. Olympian, relied on his overpowering serve despite playing lethargically at times.

Second-seeded Kei Nishikori, Japan's top player and the highest ranked player ever from his country - at No. 18 on the ATP Tour - also won his opening match, defeating Igor Sijsling from The Netherlands 6-4, 6-4.

Isner is slated to face Nicolas Mahut in the second round match. The pair met in the longest match in tennis history - 11 hours, 5 minutes before Isner's 70-68 fifth-set victory in 2010 at Wimbledon.

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