Houston, TX (SportsNetwork.com) - Sam Querrey advanced after Marinko Matosevic's retirement, and former world No. 1 Lleyton Hewitt fell to Go Soeda as the U.S. Men's Clay Court Championship commenced Monday at River Oaks Country Club.

Querrey, the No. 8 seed, was leading 4-1 in the first set when a foot injury caused Matosevic to retire after 18 minutes. Querrey was the runner-up in Houston in 2010.

Soeda defeated Hewitt, the winner of this event in 2009, 4-6, 7-6 (7-3), 6-3.

Also on Day 1, Argentine Federico Delbonis beat Lithuanian Ricardas Berankis 6-2, 7-6 (7-5) and Aussie Sam Groth stopped Dominican Victor Estrella Burgos 7-6 (7-3), 6-4.

This week's top seeds are Spaniards Feliciano Lopez and Roberto Bautista Agut. Lopez will open up against the aforementioned Groth.

Fernando Verdasco beat back-to-back runner-up Nicolas Almagro in last year's all-Spanish finale.

The winner of this tournament will receive $88,800.