New Haven, CT -- (Sports Network) - Top-seeded Fernando Verdasco doused Dudi Sela in straight sets under the lights on Monday in the only second-round match at the $708,000 Pilot Pen Tennis event, a final U.S. Open tune-up.

Verdasco downed Sela 6-4, 6-4 to move into the third round. American wild cards Robby Ginepri and John Isner were among the Day-2 first-round winners, while red-hot Argentine Juan Martin del Potro withdrew here on Monday, citing exhaustion.

A third-seeded del Potro has won his last 19 matches, with titles coming in his last four events. He's now up to No. 17 in the world.

"It is difficult to still play a lot of matches," del Potro said. "I want to recover for the U.S. Open. Unfortunately, I have to pull out of this tournament."

American Jesse Levine will replace del Potro in the draw.

Ginepri grounded Peruvian Luis Horna 7-6 (7-4), 6-2, while the 6-foot-9 Isner got past Russian Igor Kunitsyn 6-4, 6-4 on the hardcourts at the Connecticut Tennis Center.

Another American advanced Monday when Wayne Odesnik toppled veteran Frenchman Sebastien Grosjean 7-5, 6-4, while France got a win when pesky Arnaud Clement erased Brazilian Thomaz Bellucci 6-4, 6-4.

Last week's Washington, D.C. runner-up Viktor Troicki of Serbia won for the fifth time in six matches by holding off American qualifier Alex Bogomolov Jr. 7-5, 2-6, 6-1.

In other opening-round action, Slovenian qualifier Luka Gregorc defeated Paraguayan qualifier Ramon Delgado 6-2, 3-6, 6-0; Belgian Steve Darcis beat American Vincent Spadea 7-5, 5-0, retired; German Denis Gremelmayr overcame Brazilian Marcos Daniel 3-6, 6-3, 6-3; Belgian Olivier Rochus handled Russian Evgeny Korolev 6-4, 6-4; Italian Potito Starace stopped Czech Jiri Vanek 6-2, 7-6 (9-7); Spaniard Guillermo Garcia-Lopez bested Aussie Chris Guccione 7-5, 6-3; and Italian Fabio Fognini erased Ecuador's Nicolas Lapentti 6-4, 4-4, retired. The qualifier Spadea quit with a lower back injury against Darcis, while Lapentti gave way to a left knee injury versus Fognini.

American James Blake beat compatriot Mardy Fish in last year's hardcourt final here. Blake, who also titled here in 2005, is not defending his title this week.

The 2008 U.S. Open will commence next Monday in New York.