DELRAY BEACH, Fla. — Second-seeded Mardy Fish advanced to the second round of the Delray Beach International Tennis Championships on Tuesday when Bjorn Phau retired from their first-round match because of illness, while trailing 0-5.

DELRAY BEACH, Fla. — Second-seeded Mardy Fish advanced to the second round of the Delray Beach International Tennis Championships on Tuesday when Bjorn Phau retired from their first-round match because of illness, while trailing 0-5.

Fish, who grew up in South Florida and won the Delray Beach title in 2009, won 20 of 26 points in the 20 minutes he spent on court. Fish was also a finalist at the tournament in 2003.

"I've been out here long enough to know not to take these kinds of matches for granted and move on," said Fish, who has been battling thyroid illness since November. "Lord knows, I haven't been feeling the best the past couple of months.

"It causes fatigue, muscle soreness and you're susceptible to heat."

Kei Nishikori of Japan, who won his only career title here in 2008, beat Brian Dabul of Argentina 6-2, 7-6 (5).

Nishikori, returning from elbow surgery in August 2009, will play James Blake in the second round.

Juan Martin del Potro of Argentina, working his way back onto the tour after right wrist surgery last year, had a 6-4, 6-1 first round win over Richard Berankis of Lithuania.

Once the 2009 U.S. Open champion secured the opening set, he took control of the match. He only allowed Berankis to hold serve once in the second set, in the fourth game.

Six players from the scheduled main draw have come down with flulike symptoms.

Top seed Andy Roddick pulled out of the event on Monday. Radek Stepanek of the Czech Republic withdrew over the weekend. American Ryan Harrison was sick on court and lost his match on Monday.

On Tuesday, Phau and Jan Hajek of the Czech Republic abandoned matches feeling sick, and Michel Przysiezny of Poland never made it to the court.

Sixth-seeded Janko Tipsarevic of Serbia, making his first career appearance in Delray Beach, captured a tough 7-6 (14), 7-6 (1) first round victory over Ivo Karlovic of Croatia.

Karlovic, who lives in South Florida, lost in last year's Delray Beach final to Ernests Gulbis of Latvia. Gulbis is not attempting to defend his Delray Beach title.

Dubai Championships

At Dubai, United Arab Emirates, Roger Federer won his first match since losing in the Australian Open semifinals by beating Somdev Devvarman of India 6-3, 6-3 in the first round of the Dubai Championships.

Novak Djokovic, who beat Federer in Melbourne and went on to his second Grand Slam title, won his Dubai opener against Michael Llodra of France by the same score.

Federer, a four-time winner of Dubai, had his share of unforced errors but was never really in trouble in his first match with Devvarman. He saved the only two break points he faced and often brought a packed center court crowd at the Aviation Club to its feet with some stunning shots.

Djokovic, the two-time defending champion in Dubai but seeded second to Federer, also had an easy time with Llodra, losing his serve only once.

Also, seventh-seeded Marcos Baghdatis of Cyprus retired against Andrey Golubev of Kazakhstan because of the flu while trailing 4-0 in the first set.

On Monday, fifth-seeded Ivan Ljubicic of Croatia withdrew in the second set with a leg injury against Ukrainian qualifier Sergei Bubka.

The 20th-ranked Baghdatis said he has been in bed with a high temperature for the past five or six days and had been on the practice court for only about 10 minutes. He said he felt better heading into the match but then "had no energy" once he started playing.