(FORTUNE Magazine) – Mid-January: Maybe I've watched too many lawyer shows, but I've been expecting something a little more dramatic as the government finally rests its case in the Microsoft antitrust trial. Instead, the moment seems oddly anticlimactic. It takes place on Wednesday, Jan. 13. Just after the lunch recess, David Boies, the chief prosecutor, enters a large number of documents into evidence and then he says matter-of-factly, "With the admission of those materials, the United States rests." No fanfare, no fireworks. Though John Warden, Microsoft's chief litigator, offers a motion to have the case dismissed, he quickly adds that he doesn't expect Judge Thomas Penfield Jackson to rule on it; with a wry smile, the judge tells Warden he's guessed correctly. Fifteen minutes later, the first of Microsoft's 12 witnesses is sworn in. Although nine high-level Microsoft executives are scheduled to testify, the company has decided to open with its expert economist, Richard Schmalensee, acting dean of MIT's business school.

After weeks of dwindling crowds--and reporters complaining that there was no news coming out of the trial--the courtroom is packed again, and anticipation is high. Why? Not, Lord knows, because we expect news from an economist. Rather it's because now, ironically, after he's rested the government's case, Boies is really about to take center stage. We're about to have the pleasure of watching Boies, perhaps the most celebrated corporate litigator of his generation, give a clinic in cross-examination.

On some level, of course, Boies, 57, has been on center stage ever since antitrust chief Joel Klein brought him on board in late 1997. (Boies, who spent some 30 years at the big white-shoe firm Cravath Swaine & Moore, is building a new firm. He's charging $50 an hour to lead the trial team--"the bargain of the century," says one government official.) Along with Bill Gates and Judge Jackson, Boies has become a dominant figure in this trial. It was he who asked Gates most of the deposition questions that the Microsoft CEO so embarrassed himself trying to avoid answering. In October, Boies gave an opening statement that was an absolute showstopper; it still ranks as the trial's most riveting moment. Throughout, he has been the government's public face, crisply spinning each day's testimony for the television cameras. He has also turned out to be surprisingly accessible--even showing up at the Thursday night get-togethers of the trial press corps, much to the consternation of flacks on both sides, who worry he'll say something he shouldn't. (Alas, he never does.) Even the Microsoft hands will concede privately that, as one put it to me, "David is the best thing the government's got going for it."

Yet as long as the government was presenting its case, Boies' courtroom role was circumscribed. Because Judge Jackson had decreed that all direct testimony be submitted on paper ahead of time, Boies was deprived of the chance to shape the testimony through his questioning. Instead, he had to sit and watch Microsoft's lawyers try to tear apart each government witness during cross-examinations. Now that it's Microsoft's turn to make its case, the situation is reversed. Now it's Boies who gets to attack, to take over the cross-examination--which is where a lawyer earns his money and gains his reputation. Boies' record as a corporate litigator is spectacular, but aside from that opening statement, he hasn't had much opportunity to shine in this courtroom.

As Boies begins his cross of Schmalensee, we see immediately that he has a completely different technique from that employed by the Sullivan & Cromwell lawyers representing Microsoft. For starters, he doesn't waste time. Sullivan's Michael Lacovara took 45 minutes to introduce into evidence several long-ago cases in which the expert opinion rendered by the government's chief economist failed to carry the day; Boies, instead, simply asks Schmalensee, "You've had some of your economic testimony accepted and some of your economic testimony rejected by courts. Correct, sir?" "Yes," replies Schmalensee. Point taken.

Boies also feels no need--thank goodness!--to pick apart testimony page by tedious page, which in Schmalensee's case would mean picking apart 325 pages. "I want to get to the handful of central points that are at issue, while pausing to hit items that illustrate problems with the testimony," he says. "I don't want to nibble at the edges." Microsoft's lawyers tried to undermine the credibility of government witnesses by doing just that; they scored points, but it often seemed frivolous. Boies scores points too--and his seem to go to the heart of the case.

The simple, devastating way he does this is to use the witness' own words as rope for a noose. He trots out a handful of opinions Schmalensee rendered in other lawsuits--including other Microsoft litigation--in an effort to show that the witness is little more than a hired gun whose opinions are, shall we say, adjustable. For instance, one key Microsoft contention is that despite its 90%-plus share of the desktop operating system market, it does not have monopoly power. In defending this view, Schmalensee actually has the gumption to claim that there is no such thing as an "operating system market." (He says the relevant market is a broader market for "platforms.") But Boies pulls out Schmalensee testimony in another Microsoft case, from just this past fall, in which the economist defined the relevant market far more narrowly. Schmalensee is reduced to bobbing and weaving, and everyone, including Judge Jackson, can see that's what he's doing.

Even more brutal is the way Boies throws Schmalensee's answers back at him, repeating and narrowing his questions--often using the economist's own phrases--until the witness backs into a corner. "Let me rephrase the question, using your words," Boies will say--and you can almost feel the noose getting tighter. The testimony of any economist in an antitrust trial is necessarily heavy sledding, yet the exchange is never dull. Boies insists that he frowns on showiness. ("I never want people to say, 'That's a great lawyer.' I want them to say, 'He sure has a great case.' ") but he is too much the showman to let his audience get bored. And every time he scores a hit, he breaks into a wicked grin.

Over the next few days, the Microsoft team will complain that all Boies does is play word games--that he doesn't understand the technology. But they do not deny his effectiveness; indeed, watching Boies work over the MIT economist, I feel, for the first time since this trial started, some sympathy for Gates. It must be terrifying to know that whatever you say, Boies will use your words to string you up. No wonder Gates went to such lengths to duck Boies' questions!

"He's good," admits a Microsoft hand during a recess--a recess that occurs just after Boies has forced Schmalensee to admit that there is currently no viable alternative to Windows for computer manufacturers. "And you know he's just getting warmed up for Maritz," adds another member of the Microsoft team. Paul Maritz is a top Microsoft executive whose name is on more e-mail evidence than anybody's but Gates'.

He's up next.