Cox's standing is roughly tied with state Treasurer John Chiang, a Democrat who has raised several million dollars and is aggressively campaigning across the state. Chiang had 12 percent support. Former state schools chief Delaine Eastin, also a Democrat, lagged far behind at 4 percent.
The top picks among independent voters -- a growing share of the California electorate -- were Newsom and Villaraigosa. Twenty-seven percent backed Newsom and 26 percent chose Villaraigosa. Among Republican candidates, Allen won 13 percent of independents compared with 8 percent for Cox.
Newsom dominated across racial groups and genders, with the sole exception of Latino voters, who favored Villaraigosa, the former Los Angeles mayor, by nearly two to one.
The group is pivotal to Villaraigosa's campaign. The same goes for voters in Southern California, where Villaraigosa leads in Orange and San Diego counties as well as the Inland Empire region.
Voters in Los Angeles County, where Villaraigosa made his name in politics and a linchpin of his path to the governor's mansion, were split between the two leading candidates. Newsom and Villaraigosa were effectively tied at about 20 percent each among registered voters. Up north, on Newsom's home turf, the former San Francisco mayor swamped Villaraigosa, with support from more than 53 percent of registered voters in the Bay Area compared with Villaraigosa's 6 percent.
The field is not settled, with former GOP Rep. Doug Ose considering entering the race.
It's the most competitive contest in California since 2010, when billionaire Meg Whitman spent more than $178 million -- including $144 million of her own money -- trying unsuccessfully to stop Jerry Brown from returning to the governor's mansion. Brown, who also was governor from 1975 to 1983, is finishing his second term of this era and remains the most popular elected official in the state with a 44 percent job approval rating.
In the U.S. Senate race, Feinstein's bid for a fifth full term was expected to be a sleepy affair until state Senate leader Kevin de Leon announced he would attempt to unseat his fellow Democrat.
Feinstein, who has represented California in the Senate for a quarter-century, is known for her measured tone and approach. But she has drawn criticism from liberal voters over her strategy in dealing with Trump, notably her call for "patience" with his presidency earlier this year.
De Leon -- along with potential Senate candidate and billionaire Democratic donor Tom Steyer -- have seized upon such remarks as they try to capitalize on Trump's deep unpopularity among California Democrats.