The poll found Fiorina has the support of 37 percent of GOP primary voters, with 22 percent of respondents backing Campbell. Irvine Assemblyman Chuck DeVore came in a close third with 19 percent support, with 20 percent still undecided.
Forty-two percent of GOP respondents said Fiorina was the best bet for defeating Democratic U.S. Sen. Barbara Boxer in the fall, with Campbell and DeVore polling at 22 percent and 12 percent, respectively.
That could be a blow to Campbell's recent pitch that he's better poised to beat Boxer, a claim he made based on the results of hypothetical match-ups in the recent USC-LA Times poll.
The poll surveyed 511 likely GOP primary voters between May 27 and June 2. The margin of sampling error is plus or minus 4.5 percentage points.
IMAGE: U.S. Senate candidate Carly Fiorina speaks to reporters at the Sacramento Bee Capitol Bureau in Sacramento on March 26. Randall Benton/SacBee.