Big-servers John Isner and Canadian Milos Raonic 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 the third-seeded Raonic blasted 26 aces before overcoming Aussie Matthew Ebden 3-6, 6-3, 7-5.

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.

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.