NEWPORT, R.I. (AP) -- Top-seeded John Isner heard the crowd's reaction and had to take a quick peek to see what the radar gun recorded on his serve late in the match.
Isner overpowered fellow American Austin Krajicek for a 6-3, 6-3 victory Wednesday, advancing to the quarterfinals at the Hall of Fame Tennis Championships for the fourth straight year.
Leading 4-3 in the second set, Isner hit a 140 mph ace to go up 40-30 in the eighth game.
''I hit the one 140 and heard the crowd 'oohing and ahhing,' so I looked,'' he said after raising his career record on Newport's grass courts to 15-3. ''I went after the next one and I think the gun was a little off.''
On the next serve, Isner hit a slicing one clocked at 119 mph - that Krajicek returned wide.
The 6-foot-10 Isner is seeking his third title in four years. He captured the 2011 and 2012 tournaments before Lleyton Hewitt snapped his 13-match winning streak in last year's semifinals.
Isner didn't double fault at all during the match and won 24 of his 28 first-serve points.
''It went well. It was better than (Tuesday), I thought,'' he said. ''It was pretty clean match, I thought. I got up early in both sets. For me that helps so much. I feel like I play pretty well when I play ahead.''
The 29-year old Isner is the highest ranked player in the field, entering the week at No. 12. He next faces good friend and No. 7 seeded Jack Sock, a 7-5, 6-2 winner over fellow American Rajeev Ram.
Second-seeded Ivo Karlovic of Croatia edged Sergiy Stakhovsky of the Ukraine 7-5, 7-6 (3) and No. 3 seeded Hewitt of Australia beat qualifier Ante Pavic of Croatia 6-2, 6-2 in 65 minutes - half the time it took him to advance in a three-set match a day earlier.
''It was just more that I was adjusted to the courts and how they were playing today,'' Hewitt said. ''I felt I went out there with really good tactics today and executed them well.''
In other second-round action: defending champ Nicolas Mahut of France, the fourth seed, beat qualifier Luke Saville of Australia, 6-4, 6-2; Samuel Groth of Australia edged Malek Jaziri of Tunisia 7-6 (7), 7-6 (3); Dudi Sela of Israel needed just 50 minutes to defeat No. 8 seeded Adrian Mannarino of France, 6-3, 6-1; and No. 6 seeded Steve Johnson advanced when Japan's Tatsuma Ito retired with a left knee injury and Johnson leading 6-3, 2-0.