The former world No. 2, who made a visit to the American Airlines Center to watch his buddy Dirk Nowitzki play, needed only an hour to post a 6-3, 6-2 victory over Italy's Seppi in the $125,000 ATP Tour Challenger event. Haas, 33, will face France's Nicolas Mahut in Thursday's second round at the Four Seasons Resort and Club in Las Colinas.
The German, trying to recover from a succession of injuries over the last two years, is playing as a wild card in his first event on the Challenger Tour since 1996 and cruised past Seppi after watching Nowitzki lead the Mavericks to a win Tuesday night over Washington.
James Blake, like Haas a former top-10 player trying to recover from injury, was forced to withdraw from the tournament thanks to a lingering problem with his knee. Factor in losses Wednesday for Ryan Sweeting (to No. 6 seed Dudi Sela of Israel) and Bobby Reynolds (to No. 8 seed Lukas Lacko of Slovakia), and 128th-ranked Michael Russell of Houston is left as the only American still alive in the 32-player draw. Russell plays Gilles Muller of Luxembourg in Thursday's second round.
The tournament's top seed, Marin Cilic of Croatia, advanced with a 7-5, 6-3 win over Italy's Simone Botelli. Sela rallied from deficits of 3-1 and 5-3 in the third set to complete a 1-6, 7-5, 7-5 victory over Sweeting.