Google CEO Larry Page spent nearly an hour in a federal courtroom deflecting questions about his role in a copyright dispute over some of the technology in his company's Android software for smartphones.
The taciturn Mr Page often looked uncomfortable on the witness stand as he sparred with David Boies, a tenacious lawyer who grilled former Microsoft CEO Bill Gates in an antitrust lawsuit filed by the US government in the 1990s.
In this trial, Mr Boies is working for Oracle, which accused Google of building its Android software by stealing pieces of the technology from Java, a programming platform that Oracle now owns.
Mr Page rarely looked at Mr Boies and frequently said he could not remember seeing some of the internal Google documents that Oracle is using to build its case.
Mr Page sported a suit and a tie, a departure from his usual casual attire. He testified briefly on Tuesday as Oracle's witness before the trial at the US District Court in San Francisco recessed for that day.
On Tuesday, Oracle CEO Larry Ellison acknowledged he wanted to compete against Android in the smartphone market before deciding instead to sue his potential rival for copyright and patent infringement.
Google sought in opening statements to frame the case as Oracle's response to its own failure to build mobile software.
Android now powers more than 300 million smartphones and tablet computers.
The trial began on Monday and is expected to last up to 10 weeks.