Haas advances to 2nd round

Hours later, fourth-seeded Kei Nishikori of Japan became the third player to retire from a first-round match, when he pulled out in the first set against 150th-ranked Ivo Karlovic of Croatia due to a back injury.

On a breezy day with occasional light rain, the two split the first two sets. Sijsling won the first 7-5 and Haas took the second at 6-4, before the Dutchman called it quits.

The 74th-ranked Sijsling hit a return in the ninth game and crumbled to the floor with the injury. After the trainer came to the court, Sijsling went back out. Haas held onto his serve and then Sijsling was serving at 4-5 in the second set.

Frustrated at going behind 0-30, Sijsling belted three balls into the stands, hitting a spectator with one of the balls. He received a code violation warning, lost his serve which evened the score at one set apiece, and retired from the match.

"What a strange match," Haas said. "At 4-all, first point, I saw him falling to the ground. Sometimes you don't know how to react when someone is injured, but he looked like he was in pain. The first couple of points went my way and he started to smash balls out of the stadium and hit a spectator. You never want to win a match like that. It's not a proud win for me."

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

Nishikori, who won last week's Memphis title, was about to serve with Karlovic leading 5-4 in the first set when Japan's best player abandoned the match. Earlier in the set, Nishikori called for the trainer to come out and work on his back.

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.

Seventh-seeded Feliciano Lopez of Spain, who lost to Nishikori in the Memphis final, withdrew from the tournament with a left wrist injury.

On Monday night, Michael Russell retired in the second set of his match against fellow American and third-seeded Sam Querrey.