DELRAY BEACH, Fla. (AP) -- Second-seeded Tommy Haas of Germany advanced to the second round of the Delray Beach International Tennis Championships when Igor Sijsling of the Netherlands retired from their match Tuesday with an injured left ankle.

Sijsling won the first set 7-5, and Haas took the second at 6-4 before the Dutchman called it quits.

Haas will next face Denis Istomin of Uzbekistan. Istomin defeated Benjamin Becker of Germany 6-7 (3), 6-4, 7-5.

Qualifier Ernests Gulbis of Latvia, who won first ATP tour title at Delray in 2010, beat American veteran James Blake 6-1, 6-4.

Ryan Harrison lost to qualifier Daniel Munoz-De La Nava of Spain 6-2, 1-6, 6-3, squandering a 3-1 lead in the final set. Jack Sock, a wildcard into the main draw, beat Mathew Ebden of Australia 6-3, 6-3.

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