Wearing a dark suit and gray tie instead of a baseball uniform and spikes, Roger Clemens strode into a federal courtroom Wednesday morning for the most consequential performance of his life.

He took a seat at the defense table in Courtroom 16, where the legendary former baseball star is being tried on charges he lied to Congress about having taken steroids during his playing days. As the trial began, prosecutors said Clemens used performance-enhancing drugs to extend his career, then lied to preserve his image; his defense team said he was clean throughout his 24-year career, and never lied.

As he did when he took the mound as a ballplayer, Clemens drew a crowd. By 8 a.m., a long line of law clerks, attorneys and tourists had formed outside the courtroom in the District’s federal courthouse. A second courtroom, where the proceedings were broadcast via closed-circuit television, was also filled to capacity.

Some came to catch a glimpse of the former pitcher known as the “Rocket.” Others wanted to hear opening statements in the high-stakes trial, the second federal prosecution of a former major league star charged with lying about his use of performance-enhancing drugs this year. Charged with perjury, obstruction of Congress and making false statements, Clemens could face a maximum of 30 years in prison if convicted of all charges.

Federal prosecutors quickly sought to establish Clemens, an 11-time All Star, as a cheater who took steroids and Human Growth Hormone to recover from injuries and lengthen his career. Clemens then lied to a House committee about using the substances in an attempt to preserve his legacy and his chances of making the Hall of Fame, Assistant U.S. Attorney Steven Durham said during opening statements.

Defense lawyers called Clemens one of baseball’s hardest-working pitchers, a fireball-throwing right-hander who never used performance-enhancing drugs — and, therefore, never lied about it. “There was a rush to judgment on Roger Clemens that has made it impossible for him to be judged fairly until today,” said his lead attorney, Rusty Hardin.

Hardin also tried to pivot jurors’ attention to the man expected to be the government’s star witness: Brian McNamee, the pitcher’s former trainer. Hardin said McNamee — who testified before Congress that he had injected Clemens with performance-enhancing drugs with the pitcher’s knowledge — is not to be trusted.

McNamee has admitted to lying to investigators in a 2001 police investigation and his story about steroids has changed over the years, Hardin alleged.

“Brian McNamee is a liar,” Hardin said. “Roger Clemens’s only crime was having the poor judgment of staying connected to Brian McNamee.”

Now 48, Clemens is considered one of baseball's all-time greats, a seven-time Cy Young Award winner who pitched for the Boston Red Sox, New York Yankees, Toronto Blue Jays and Houston Astros.

Even if acquitted, he has joined a list of players once considered surefire Hall of Fame inductees — including Barry Bonds, Mark McGwire, Rafael Palmeiro and others — whose associations with performance-enhancing drugs, whether admitted or alleged, have darkened their sporting legacies and the image of Major League Baseball.

Bonds went on trial earlier this year on charges of lying to a grand jury about his own steroid use. The jury hung on every count but one, convicting the former slugger of one count of obstructing justice.

Major League Baseball has prohibited the use of steroids and HGH without a prescription since 1971. It explicitly banned steroids in 1991 and HGH in 2005.

The trial opened Wednesday after four days of intense jury selection that resulted in a panel of 10 women and two men. One federal prosecutor opened his case by explaining why Congress had launched an investigation of performance-enhancing drugs and why Clemens then testified before a House panel in 2008.

In late 2007, former Sen. George Mitchell issued a 409-page report on behalf of Major League Baseball that identified dozens of players, including Clemens, who had taken the banned substances. The pitcher quickly denied the allegations, Durham said.

Because lawmakers worried that children might be influenced by the players’ conduct — and because they wanted “to see if Mitchell had got it right,” Durham said — the House Committee on Oversight and Government Reform invited Clemens to testify on national television.

Clemens accepted. But his testimony was “false and he knew it was false,” Durham said. To prove his case, Durham said, he will introduce a mound of evidence and call 45 witnesses including Andy Pettitte, another former star pitcher and Clemens friend and teammate who has admitted taking HGH. Pettitte told Congress that Clemens had admitted to him that he had also taken the same drug.

Pettitte is important, but the case largely rests on McNamee, the former trainer sure to be assailed by defense lawyers on the stand. Even so, Durham promised jurors that they would not have to “hang your hat on the word of one man over another.”

“Everything Mr. McNamee says, we intend to corroborate,” he said.

Part of that corroboration involves needles obtained from McNamee that the former trainer said he used to inject Clemens with steroids in August 2001, Durham said. Forensic tests have revealed that those needles contained traces of Clemens’ DNA and of steroids, the prosecutor said publicly for the first time.

When Hardin got his chance, he alleged that McNamee could have fabricated that evidence. He also blasted prosecutors’ allegation that Clemens used performance-enhancing drugs to stretch out his career.

Clemens went on to play six seasons after McNamee is last alleged to have injected the pitcher with steroids, Hardin told jurors.

“If Roger Clemens is taking steroids to prolong his career, why in the world would he continue to play for six more years without the suggestion from anyone that he used steroids?” Hardin asked.

Prosecutors called their first two witnesses — a former House parliamentarian and a House staffer — Wednesday afternoon. They testified that Congress had the authority to hold hearings about the prevalence of steroids in baseball. Clemens’s lawyers have challenged the validity of the Congressional hearing in 2008 that pitted Clemens against McNamee.

Hardin asked Charles W. Johnson, the former parliamentarian, pointed questions about the hearings. “What legitimate investigative purpose is served by asking a private citizen if they ever used a controlled substance?” Hardin asked.