Another wealthy businesswoman, former Hewlett-Packard Co. CEO Carly Fiorina, was leading in early returns in the Republican primary to decide who will challenge Democratic Sen. Barbara Boxer in the fall.
If Fiorina wins, it would be the first time the California Republican Party would have put a woman -- much less two -- at the top of its ticket.
It also will set off an election season of big-money campaigns and high drama in the nation's most populous state, pitting two deep-pocketed Silicon Valley business stars against stalwarts of the Democratic Party establishment.
Whitman, 53, worked on the presidential campaigns of Mitt Romney and John McCain. She has spent much of the primary in tightly scripted appearances and was criticized early on for avoiding detailed questions from political reporters. On Tuesday, Brown took a swipe at Whitman's reputation for controlling her message.
"I'm looking forward to a campaign where people get to see the candidates, not just the commercials," he said.
The opponent Whitman beat Tuesday, state Insurance Commissioner Steve Poizner, is a wealthy Silicon Valley entrepreneur who spent $25 million of his money on his race.
The heated battle with Poizner to win over conservative GOP primary voters forced Whitman to move to the right on issues such as abortion and illegal immigration, moves that could hurt her against Brown in November.
Democrats and moderate independents comprise two-thirds of the electorate in California. Without a serious primary challenger, Brown has positioned himself as a moderate, pledging not to raise taxes and to make the kind of spending cuts that Whitman also campaigned on.
The gubernatorial race promises to be the most expensive in state history.
Brown will not be able to match Whitman's millions -- he has $20 million in the bank so far -- but is relying on Democratically aligned independent groups to fund an opposition campaign.