Capriati fell 6-0, 7-5 to Poland's top player, Magdalena Grzybowska, in the first round of the Lipton Championships in Key Biscayne.
Capriati, ranked sixth in 1992-93, has lost seven straight matches and has been beaten n six consecutive first rounds, dating to her last victory in August 1997 at the Canadian Open.
"I felt nervous, anxious going out there," said Capriati, who was returning after taking five months to recuperate from a shoulder injury.
Indeed, Capriati, who was arrested on drug and shoplifting charges several years ago, looked nervous as she sprayed her shots wildly over the court in the first set that she lost on two double faults.
But the 21-year-old, now ranked 147th, settled down in the second set and fought off a match point at 4-5 to hold at 5-5 before spraying a forehand long on the second match point in the 12th game.
Serena Williams, one of the newer teenage female players, gained an easy 6-4, 6-0 win over Denise Chladkova of the Czech Republic.
Before play began on Thursday, the five-times winner Steffi Graf and the reigning French Open Champion Iva Majoli withdrew from the tournament. A hamstring injury suffered last week forced Graf to withdraw, while Majoli pulled out because she has the flu.
Greg Rusedski, the British No 1 and the No 5 seed, who was given a bye in the first round, will play the Slovak Dominik Hrbaty, ranked No 52 in the world. Hrbaty defeated the Czech Daniel Vacek 6-3, 6-2. Boris Becker has withdraw from the tournament because of flu.