Andy Roddick's unconvincing form at the Atlanta Tennis Championships continued as he was again taken to three sets before seeing off the determined challenge of Belgium's Xavier Malisse in the quarter-finals.
The top-seeded Roddick was taken to a decider by fellow American Rajeev Ram in the last round of the hard-court event and was again given a stern test by seventh seed Malisse before eventually prevailing 4-6 6-3 6-4.
Next up for the former world No.1 one is a semi-final encounter with sixth-seeded compatriot Mardy Fish, who defeated another American, Taylor Dent, 6-3 6-0 in the day's late game.
Second-seeded American John Isner finally enjoyed the luxury of a swift conclusion to a match as he dominated countryman Michael Russell in a one-sided 6-1 6-2 win.
Isner was taken to three sets by Gilles Muller in the last round in his first game back since Wimbledon, where he hit the headlines by winning an epic 11-hour match with Nicolas Mahut, but had no such concerns against Russell, winning in just 56 minutes.
South Africa's Kevin Anderson awaits Isner in the last four after he posted a 6-3 6-4 win over Slovakia's Lukas Lacko.
Meanwhile third seeded Austrian Jurgen Melzer booked his place in the semi-finals of the German Open in Hamburg with a 69-minute 6-4 6-1 victory over Italy's Potito Starace.
The in-form Melzer, who reached the French Open semi-finals earlier in the clay-court season, will next face another Italian, Andreas Seppi, who edged an epic contest 7-6 (7-0) 5-7 7-5 over Brazil's Thomaz Bellucci.
Juan Carlos Ferrero's hopes of winning his third tour title of the year were ended by home favourite Florian Mayer, who came from a set down to score a 6-7 (3-7) 6-2 6-3 win over the Spanish seventh seed.
Mayer's last four opponent will be Kazakhstan's Andrey Golubev, who built on his career-best win over top seed Nikolay Davydenko by breezing past Denis Istomin of Uzbekistan 6-4 6-1.