Andy Pettitte took the witness stand just before noon in the perjury trial of his longtime friend Roger Clemens, testifying that he admired the flame-throwing right-hander since high school and later formed a close bond with him when they became teammates in the major leagues.

Pettitte, a 39-year-old pitcher who played for the New York Yankees and Houston Astros, is considered a key witness in the prosecution of Clemens on charges he lied to Congress in 2008 when he denied taking performance-enhancing drugs.

Pettitte has told Congressional investigators that Clemens confided in him in 1999 or 2000 that he had taken Human Growth Hormone (HGH). Prosecutors allege that Clemens was injected with steroids or HGH in 1998, 2000 and 2001 by his former strength coach, Brian McNamee, who is also expected to testify in the trial.

Pettitte has admitted that he took HGH to help him recover form an elbow injury in 2002.

In just over 30 minutes of questioning by Assistant U.S. Attorney Steven Durham, Pettitte described his life and career and how he came to know Clemens. Wearing a gray suit, Pettitte spoke in a southern drawl, answered most questions with one-word responses and seemed reluctant to be on the stand.

He described growing up in Deer Park, Texas, and his ascent into the big leagues and his admiration for pitchers like Clemens, Jim Abbott and Nolan Ryan – all stars in their day.

In 1996, while pitching for the New York Yankees, Pettitte met Clemens for the first time in the outfield of Boston’s Fenway Park, where the two pitchers were set to square off against each other. Clemens, who was then playing for the Boston Red Sox, approached Pettitte and wished him luck.

“It was great,” Pettitte said of meeting his future friend. “It fired me up. It was meeting somebody you looked up to, watched since high school. It was awesome.”

By 1999, they were teammates on the Yankees and later on the Astros, which play in Houston, the area where both Clemens and Pettitte reside. They became close friends and are known to have played golf and worked out together. It was during one of those workout sessions that Clemens allegedly confided to Pettitte that he had taken HGH, prosecutors allege.

Just before his testimony ended for a lunch break, Pettitte answered “yes” to several questions by Durham about how baseball’s long season can take a “toll” on a pitcher’s body and joints.

The questions are likelysetting up a discussion by Pettitte about why he was talking to Clemens about performance-enhancing drugs and why he decided to take the substances.

Pettitte, who retired in 2010, is trying to make a comback with the Yankees. He testified that the Yankees were “seriously interested” in him taking the mound again; the left-hander gave up six runs on 10 hits in just six innings in his most recent outing, an extended spring training game in Florida.

Clemens is being prosecuted by the Justice Department on charges he committed perjury, obstructed Congress and made false statements in testimony to the House Committee on Oversight and Government Reform in 2008. Clemens denied using steroids or HGH to Congressional investigators and druuing a nationally televised hearing.

The investigation followed a 2007 report by former senator George Mitchell that identified Clemens and dozens of other players as having taken banned substances.

Major League Baseball has since 1971 prohibited the use of steroids and human growth hormone — known as HGH — without a prescription. The league explicitly banned steroids in 1991 and HGH in 2005.

Read more: Clemens trial coverage | Del on Twitter