Top seed Roger Federer survived a scratchy performance to beat Marcos Baghdatis of Cyprus 7-6, 7-5 on Thursday to reach the quarter-finals of the Cincinnati Masters.
But holder Andy Roddick went out, losing 7-6, 6-4 to 16th seed David Ferrer of Spain.
In stifling humidity with the on-court temperature more than 100 degrees (37.7 Celsius), Federer saved four set points at 6-5 down in the opener.
The Cypriot spurned two set points with double-faults before Federer eventually took the tiebreak 7-5.
Baghdatis was broken in the third game of the second set. He drew level at 5-5, only to lose his serve in the next game as Federer went on to clinch a meeting with Spaniard Nicolas Almagro, a 6-2 6-2 winner over Finn Jarkko Nieminen.
"It was a struggle out there," Federer told reporters. "It was tough to keep the ball in play and they were really quick conditions.
"I am just really happy I got through."
Roddick looked in control early on but was frustrated by brilliant retrieving from Ferrer, who forced him further and further back behind the baseline.
The American was made to pay for missing three set points in the 10th game as Ferrer took the tiebreak and then broke in the 10th game of the second set.
ORDINARY PERFORMANCE
"I was standing too far back," said Roddick. "I wasn't imposing myself and I was giving away free points.
"It was a pretty ordinary performance (but) I'm not going to go into panic mode. I know what I did wrong today."
Ferrer next plays fifth seed Nikolay Davydenko of Russia, who hammered Czech 10th seed Tomas Berdych 6-3 6-2.
Carlos Moya set up a quarter-final against Lleyton Hewitt with a 7-5 3-6 7-5 win over Argentine teenager Juan Martin Del Potro.
World number 78 Del Potro saved four match points in the third set before the Spaniard secured victory after a successful Hawk-Eye challenge on a ball that had been called out on the baseline.
Moya, 31, the oldest player in the world's top 20, had beaten world number three Novak Djokovic in the previous round.
"I'm very happy I won because I think I was controlling it pretty well until the middle of the second set," Moya said.
"Maybe I relaxed a little bit and he took advantage of that but I was able to come back and once you get to 5-5 in the third it's 50-50."
Hewitt, ranked 20, recovered from an early break to beat Austrian Juergen Melzer 6-3 6-3.
Moya leads the Australian 6-5 head-to-head but Hewitt has won their last four meetings.
American wildcard Sam Querrey upset Juan Monaco of Argentina 6-3 7-5 and next plays ninth-seeded compatriot James Blake, who crushed Spaniard Juan Carlos Ferrero, the runner-up last year, 6-1 6-4.
