German Tommy Haas secured near-effortless passage into the third round of the Cincinnati Masters on Wednesday as France's Gael Monfils retired trailing 5-1 with a bad stomach, the dpa reported.
The French Open semi-finalist began calling for a doctor on court at the end of the third game, only able to tough it out for less than half an hour before throwing in the towel.
Haas awaits an opponent as second seed Rafael Nadal aims for a 30th straight victory, as he opens play after winning his seventh title of the season at the weekend in Toronto.
The Spaniard is facing Frenchman Florent Serra, ranked 84th.
Ecuador's veteran Nicolas Lapentti, who drifted briefly into the top ten nearly a decade ago, provided the first major surprise of the week, putting out Spanish fifth seed David Ferrer 7-6 (7-2), 3-6, 6- 3.
The upset took two and a half hours.
American James Blake, seeded seventh, ended the recent run of form of France's Gilles Simon as he beat the 14th-ranked Indianapolis champion and Toronto semi-finalist 6-3, 6-4.
British eighth seed Andy Murray played on full fitness after a minor knee worry last weekend in a defeat of American big server Sam Querrey 7-6 (7-3), 6-1.
The Scottish winner said he needed time to get used to a faster court and the Queerry game, recovering from an early break before taking complete control for a win in an hour and a quarter.
"This is a really important tournament for me and I want to do well. I've got a good chance of moving my ranking up again this week.
"I want to try and get seeded into the top eight for the US Open. That's key and I want to do better than the guys that are ranked around me."
"I've just got to try and keep winning."
Fast-rinsing Ernests Gulbis of Latvia put out French veteran Arnaud Clement 6-4, 3-6, 7-6 (7-5).