KEY BISCAYNE, Fla. -- It took just a few years for Mardy Fish to progress from the top row of the stadium at Key Biscayne to a courtside seat. And now he's into the second round of the Nasdaq-100 Open.

Fish, a hero for the United States in his Davis Cup debut last month, overcame a slow start Wednesday to cool off Michel Kratochvil 3-6, 7-5, 6-1 on the opening day of the tournament.

The son of a teaching pro in Vero Beach, Fla., Fish next plays Marcelo Rios, who won the Key Biscayne title in 1998. Fish was there, a 16-year-old watching from the cheap seats.

"Like the top row," he said. "I was like throwing stuff off the back, trying to hit people."

Fish has come a long way since, although he hasn't kept pace with good friend Andy Roddick. They lived and practiced together in Boca Raton for a couple of years before Roddick blossomed into a top-15 player in 2001.

"I'm thrilled that he's doing well," said Fish, 20. "I just need to work on my mental part of the game and my serve a little bit more and my forehand, and hopefully I can be up there just like him."

Todd Martin rallied to beat Julien Boutter 2-6, 7-6 (3), 7-6 (7). Another American, 19-year-old Robby Ginepri, lost to Juan Ignacio Chela 3-6, 6-3, 7-6 (3). Chela will next play Roddick, seeded 10th.

American winners in women's play included Lilia Osterloh and Marissa Irvin. Britain's Greg Rusedski beat Sargis Sargsian 6-3, 6-4 and advanced to a second-round match against defending champion Andre Agassi, who is seeded ninth.

Seeded players had opening-round byes and will take the court for the first time Friday.

Fish earned just his third victory this year in tournament play, but it was the fourth of his career over a top-50 opponent. Kratochvil, a Swiss youngster ranked 43rd, upset Agassi last week in the first round at Indian Wells.

Fish jokingly described his victory as "an indirect win over Agassi. ... No, it's great to beat a hot player."

Now ranked 150th, Fish teamed with James Blake in doubles last month to win the clinching Davis Cup match as the Americans beat Slovakia. That ended a five-match losing streak in doubles for the United States.

Captain Pat McEnroe will soon announce his squad for the second-round match in Houston against Spain, and Fish expects he'll give up his spot to Martin, 31.

"If I were the captain, I would pick Todd over a 20-year-old who doesn't have any experience," Fish said.

Rusedski, who holds the record for the fastest serve in ATP Tour history at 149 mph, took advantage of sunny, 83-degree weather that made the courts play faster. He hit just six aces but made 76 percent of his first serves and lost only nine points on his serve.

"When it's hot like this, you've just got to keep the percentage up and get that high kick and let the court and the ball do the work for you," Rusedski said.

With the conditions affecting the court speed, Rusedski figures he'll be scheduled to play Agassi at night. Agassi has won six of their eight matches.

"I've beaten him in the past and played him pretty tough in most matches we've played," Rusedski said. "I look forward to it. It's a challenge."

Because of a computer error, seedings for No. 2 Juan Carlos Ferrero and No. 3 Yevgeny Kafelnikov were flipped. When the mistake was discovered, they exchanged places in the draw, which means Ferrero plays Martin next.