Flushing Meadows, NY (My Sportsbook) - Andre Agassi was leading Florian Mayer when the rising German retired in the fourth set of their second-round match Thursday at the 2004 U.S. Open.

The sixth-seeded Agassi was ahead 7-5, 2-6, 6-2, 1-0 when Mayer called it quits due to a left hamstring injury at Ashe Stadium.

After losing a tough first set, Mayer played a beautiful second stanza, displaying a top-notch backhand en route to taking the set. But the young German started to show signs of the injury in the third and began to fade away as Agassi seemingly got stronger.

After the 34-year-old Agassi easily held serve to open the fourth set, the world No. 37 Mayer walked over to the chair umpire waving his hands and apologized to Agassi for his decision to quit.

The 20-year-old Mayer reached the Wimbledon quarterfinals in July.

The eight-time Grand Slam champion Agassi captured the U.S. Open in 1994 and 1999 and was the runner-up here in 1990, 1995 and 2002.

Fifth-seeded Englishman Tim Henman was tested in a 6-2, 6-4, 4-6, 7-6 (7-1) victory over French qualifier Jerome Golmard on the famed Grandstand Court.

The serve-and-volley specialist Henman surprisingly reached the French Open semis earlier this year.

Earlier in the day, surprise French Open titlist Gaston Gaudio went by way of the upset, as big-serving Swede Thomas Johansson sent the ninth seed packing in 6-3, 2-6, 6-4, 6-4 fashion at the USTA National Tennis Center.

Gaudio, who typically excels on red clay, captured Roland Garros in June by stunning countryman Guillermo Coria in an all-Argentine final in Paris.

Johansson, who missed all of the 2003 season while recovering with a knee injury, won the Australian Open in 2002.

In other action involving top-16 seeds, No. 15 Thai Paradorn Srichaphan handled American Paul Goldstein 6-4, 7-6 (7-4), 6-0 and No. 16 Romanian Andrei Pavel dismissed Spaniard Fernando Verdasco 7-5, 6-3, 7-6 (7-2).

One of this summer's hottest players, German Nicolas Kiefer, advanced to round three with a hard-fought 7-6 (7-0), 6-3, 7-6 (7-4) victory over French shotmaker Cyril Saulnier. Kiefer, seeded 19th at this hardcourt fortnight, will encounter the resurgent Johansson in the round of 32 here.

No. 22 seed Dominik Hrbaty went the distance to best his fellow Slovakian Karol Kucera 6-4, 6-3, 1-6, 5-7, 6-4.

Crafty Frenchman Fabrice Santoro blew past Russian Dmitry Tursunov 6-1, 6-3, 6-4. The 31st-seeded Santoro is rewarded with a third-round match against world No. 1 Roger Federer -- the reigning Australian Open, Masters Cup and two-time Wimbledon champ.

Other Day-4 winners were Korean Hyung-Taik Lee and Belgian Olivier Rochus.