Daniel Petrocelli is not an antitrust expert—but the O’Melveny & Myers partner didn’t need to be in order to win the biggest merger challenge in decades.

Instead, the self-proclaimed generalist relied on his tried and true skills as a litigator to convince U.S. District Senior Judge Richard Leon to approve the $85 billion union of AT&T and Time Warner without conditions, handing the Justice Department’s Antitrust Division a rare courtroom defeat.