Andy Pettitte, former friend and teammate testifies against Roger Clemens

(CBS News) Former MLB pitcher Roger Clemens faced the legal version of a pitcher's duel at federal courthouse on Tuesday and Wednesday when his former friend and teammate Andy Pettitte testified against him.

Clemens, who retired in 2007 and considered one of the game's greatest pitchers, is charged with lying to Congress in 2008 about whether he took banned substances while playing in the major league.

In his Tuesday testimony Pettitte directly contradicted his old friend. While describing a conversation in 1999 while the two men worked out at Clemens' home, Pettitte said "Clemens mentioned that he had taken human growth hormone, it could help with recovery and that's all I really remember about the conversation."

Pettitte said Clemens' comment was made "in passing." Clemens has long insisted that Pettitte "misremembers" the conversation, and has consistently denied that he used banned substances.

Under cross-examination Wednesday, Pettitte was asked if it was fair to say it was "50-50" that he misunderstood the conversation in which he claimed Clemens mentioned that he had taken human growth hormone. Pettitte replied, "I'd say that's fair."

In 2008, Clemens also denied using banned substances in an interview with Mike Wallace for "60 Minutes."

Pettitte, who at 39 has come out of retirement to attempt a comeback with the New York Yankees, did not look at Clemens in the courtroom until he was asked by a lawyer to point him out. Pettitte testified that he considered Clemens, ten years older, to be his mentor and while they haven't spoken in a long time, said he still has affection for Clemens and found it difficult to testify against him.

Commenting on the trial New York Times sports columnist William Rhodes said Barry Bonds and Roger Clemens are "fall guys" in the steroids in sports scandal.

"Bonds and Clemens are fall guys. I want to see the commissioner of baseball take the stand," Rhodes said Wednesday on "CBS This Morning." "If we really want to follow the truth where it leads, because there's a whole level of baseball execs who knew all this stuff was going on. What they're doing is throwing these guys under the bus, saying 'ok that's the end of the steroid era. Let's continue to make billions of dollars.'"

Former personal trainer Brian McNamee, who claimed he injected both Clemens and Pettitte with performance enhancing drugs, is another key witness. The trial is expected to last six weeks.

Chip Reid

Chip Reid is CBS News' national correspondent.