Former champion Tommy Haas advanced when his opponent retired Tuesday at the Delray Beach International Tennis Championships.
The second-seeded onetime world No. 2 Haas was tied with Igor Sijsling, 5-7, 6-4, when the Dutchman quit on Day 2 at Delray Beach Tennis Center.
Haas, who titled here back in 2006, will face Denis Istomin in the round of 16.
Top-seeded American John Isner defeated Jesse Levine, 7-6 (7-3), 5-7, 6-4 to advance to the second round.
Kei Nishikori, fresh off his championship in Memphis last week, was forced to retire in the first set of his match with Ivo Karlovic, the 2010 runner-up at the Delray Beach event. Nishikori, who won this event in 2008, was hampered by a back injury.
Sixth-seeded Kevin Anderson took the next step in defending his Delray Beach crown with a 6-3, 6-4 win over Tim Smyczek, while Go Soeda rallied to defeat Marinko Matosevic, 2-6, 6-4, 7-6 (8-6).
In matches involving Americans, Jack Sock whipped Aussie Matthew Ebden, 6-3, 6-3; Taiwan's Yen-Hsun Lu topped Bobby Reynolds 6-3, 7-5; Spaniard Daniel Munoz-De La Nava outlasted Ryan Harrison 6-2, 1-6, 6-3 and talented Latvian Ernests Gulbis dismissed an aging James Blake 6-1, 6-4.
Gulbis titled here in 2010, while Blake was a Delray Beach runner-up in 2007 and 2008.
Additional opening-round wins came for Uzbekistan's Istomin, Frenchman Edouard Roger-Vasselin and Lithuanian lucky loser Ricardas Berankis, who assumed a spot in the draw when seventh-seeded Feliciano Lopez pulled out just two days after finishing as a runner-up in Memphis.
The 2013 champion will pocket $78,000.