SAN FRANCISCO — Olympic gold-medal sprinter Antonio Pettigrew on Thursday for the first time admitted taking performance-enhancing substances during a long, successful track career in which he passed all drugs tests.

The admission came during testimony in the trial of his former coach Trevor Graham, who is accused of lying to federal authorities investigating doping in sports. Graham has pleaded not guilty.

Pettigrew testified that Graham encouraged him in 1997 to inject human growth hormone and the oxygen-boosting drug EPO, which are both banned in track. Soon after, Pettigrew said, he began buying the drugs from Angel "Memo" Heredia, an admitted steroids dealer from Laredo, Texas.

Once he began taking the banned substances, Pettigrew said he was able to run 400 meters in under 43 seconds for the first time.

"I was running incredible times as I was preparing for track meets," Pettigrew said during 30 minutes of testimony. "I was able to recover faster."

Pettigrew initially lied to federal investigators and denied doping when they first talked to him in February 2005. But he finally confessed to cheating when confronted with documents in October 2006 strongly suggesting drug buys from Heredia.

Pettigrew won a gold medal as part of the 1,600-meter relay team at the 2000 Sydney Olympics. He retired from track in 2002 and is now an assistant coach at the University of North Carolina.

Also Thursday, IRS agent Erwin Rogers testified that Justin Gatlin, the defending Olympic 100-meter champion and another former Graham athlete, worked undercover for the government and secretly recorded several telephone calls with Graham. U.S. District Court Judge Susan Illston barred Rogers from disclosing any more details of the calls.

Gatlin, who has served half of a four-year ban for doping, tested positive for excessive testosterone at the Kansas Relays in 2006, his second doping violation. He has maintained he never knowingly took a performance-enhancing drug.

Gatlin has asked the Court of Arbitration for Sport to cut his suspension nearly in half so he can compete at the Beijing Olympics.