Florida - Having acclimated to the Florida humidity, top seed John Isner captured a 6-3, 6-4 win over fellow American Ryan Sweeting on Wednesday to move into the quarter-finals of the Delray Beach International Tennis Championships.
The 11th-ranked Isner struggled through his first round win over wildcard Jesse Levine on Tuesday because of the humidity, but was in better shape playing Sweeting.
"Whenever, in the past, when I've played tournaments in humidity I've always struggled because I hadn't acclimated yet," Isner said. "But tonight I felt so much better than I did on Wednesday.
"I'm still not all the way there. I could feel better out there but it was so much better."
Isner's quarterfinal opponent will be Australian Bernard Tomic, who had a 6-1, 7-5 win over American qualifier Tim Smyczek.
Qualifier Marinko Matosevic made it two Australians in the last eight by upsetting sixth-seeded Alex Bogomolov Jr. of Russia 4-6, 6-1, 6-3.
It is the first time Matosevic has made an ATP quarter-final, and he will take on 2010 tournament champion Ernests Gulbis of Latvia, who defeated Belgium's Steve Darcis 6-7 (6), 6-1, 6-3.
The 173rd-ranked Matosevic had 11 aces and won five of eight break points.
"It was a tough match and I'm happy to get through and make my first quarter-final," said Matosevic. "I knew his game pretty well and he reaches a lot of balls, so I just had to keep staying aggressive. I played the big points well."
The 26-year-old has spent most of his career playing on the Challenger circuit.
Bogomolov had the best season of his career in 2011, starting the year at No. 166 and finishing at No. 34. Fellow players voted him the year's most improved player, but he struggled throughout the match, including in his victorious first set.
Gulbis reached his first quarterfinal of the season. The Latvian won 40 of 45 points on his first serve and fired 10 aces.
"Today was tough because I couldn't get my timing right in the first set," said Gulbis, who said the wind made it difficult. "From one side it was much easier to get your serve going than the other side.
"I didn't play my best tennis today but I'm happy I won the match because I was fighting."
Isner broke Sweeting's serve twice in the match - in the second game of the first set and the fifth game of the second set - which was all he needed to take the win.
Sweeting was unable to capitalize on five break points when Isner kicked his potent serve into overdrive to save the points.
"A lot of times for me to be successful I'm going to have to have my serve and I did today when I needed it," Isner said. "I served well, went for my second serve, wasn't going for broke, but I hit my spots and it got me out of a couple of jams."