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Tommy Haas took his place in the second round of the Delray Beach International Tennis Championships when Igor Sijsling was forced to retire.
The second seed had just levelled the match at 5-7 6-4 when the Dutchman, who had an awkward fall in the second set, withdrew because of an ankle injury.
Top seed John Isner also advanced as he beat Canada's Jesse Levine 7-6 (7/3) 5-7 6-4.
South African sixth seed Kevin Anderson advanced in straight sets, beating Tim Smyczek of the United States 6-3 6-4.
But fourth seed and former champion Kei Nishikori suffered a muscle injury in the first set against Ivo Karlovic and had to retire.
Another former champion, Ernests Gulbis, booked his place in the second round, beating James Blake 6-1 6-4.
The world number 109, who won here in 2010 but had to qualify this time, needed just 73 minutes to seal victory.
Other winners included Denis Istomin, Ricardas Berankis and Jack Sock.