US top seed John Isner and second-seeded defending champion Ivo Karlovic advanced to the quarter-finals of the ATP Hall of Fame Championships with straight-set triumphs Wednesday at Newport, Rhode Island.
Isner, the 2011 and 2012 winner at the grass-court event, fired 13 aces in defeating Australian qualifier Sam Groth 6-2, 6-4. The hard-serving American improved to 3-0 all-time against Groth, who dropped prior meetings in Davis Cup ties this year and last year, with the 61-minute triumph.
Croatia's Karlovic, 38, defeated American Denis Kudla 6-4, 6-4 to reach the final eight. Karlovic, seeking his ninth career ATP crown, lost the 2014 and 2015 Newport finals before downing Gilles Muller 14-12 in a third-set tie-breaker to win last year's championship match.
Isner advanced to a quarter-final matchup against fellow American Dennis Novikov, a 6-3, 6-2 winner over Canadian Frank Dancevic.
Karlovic booked a quarter-final meeting with Germany's Peter Gojowczyk, who eliminated Russia's Konstantin Kravchuk 2-6, 6-4, 6-4.
Germany's Tobias Kamke pulled the biggest upset so far, ousting French third seed Adrian Mannarino 7-6 (7/5), 7-5. He will next face Australian qualifier Matthew Ebden, who defeated sixth-seeded Slovakian Lukas Lacko 6-1, 7-6 (7/2).
Also advancing was fourth-seeded Frenchman Pierre-Hugues Herbert, who outlasted Spain's Adrian Menendez-Maceiras 7-5, 2-6, 6-3. His next opponent American Bjorn Fratangelo, who ousted Australian Akira Santillan 7-6 (7/3), 3-6, 6-1.