Big-server John Isner and former world No. 1 Lleyton Hewitt were a pair of opening-round winners Tuesday at the Hall of Fame Tennis Championships.

The top-seeded and defending champion Isner scalded 20 aces before holding off Ukrainian qualifier Sergei Bubka 7-6 (7-3), 4-6, 6-3, while Hewitt, a two-time major champion, need just 49 minutes to dispatch Canadian Vasek Pospisil, 6-1, 6-1.

The 6-foot-9 Isner beat Belgian Olivier Rochus in last year's finale on the grass courts at the International Tennis Hall of Fame.

Up next for Isner will be Frenchman Nicolas Mahut, which will mark a rematch of their epic opening-round Wimbledon match two years ago, a match that was more than 11 hours long and played out over three days at the All England Club. Isner won that one.

Second-seeded rising Japanese Kei Nishikori advanced with a 6-4, 6-4 victory over Dutchman Igor Sijsling, while unseeded American Sam Querrey ousted fifth- seeded Russian Alex Bogomolov Jr. 7-5, 7-6 (7-5). Querrey was the Newport runner-up in 2009.

Another big-server, third-seeded Canadian Milos Raonic, fired 26 aces en route to a 3-6, 6-3, 7-5 victory over Australian Matthew Ebden. Raonic double- faulted four times in the opening set, but regained his footing to secure the victory in one hour, 54 minutes.

Upsets came when American qualifier Tim Smyczek doused fourth-seeded Denis Istomin of Uzbekistan 6-3, 6-3 and South African qualifier Izak Van der Merwe dismissed eighth-seeded Gilles Muller of Luxembourg 7-6 (7-5), 6-7 (3-7), 6-4.

Rajeev Ram, who surprised Querrey in an all-American final here three years ago, handled Slovenian Grega Zemlja 6-3, 6-1 on Tuesday.

Additional Day-2 wins came for American Jesse Levine and German qualifier Benjamin Becker.