It was a closed primary. Davis had nothing to do with it.
It was a closed primary, but Davis ran ads in during the GOP primary season about Riordan flip-flopping on abortion in a successful attempt to get the conservative base to vote for the more beatable Simon. This was despite the fact that the gov. has no say in the abortion debate. Parental notification propositions are regularly defeated here and unlike the US Constitution, the CA Constitution has an express right to privacy.
So instead of having a governor like Riordan, who did a good job running LA, we got Davis.