The pair, in their first tournament together, beat second-seeded Americans Raquel Kops-Jones and Abigal Spears 7-6 2-6 10-4 in the doubles quarter-finals in Stanford.
In the semifinals, Erakovic and Watson will play either Natalie Grandi (South Africa) and Vladimira Uhlirova (Czech Republic) or the team of Eleni Daniilidou (Greece) and Urszula Radwanska (Poland).
Early tomorrow morning (NZT), Erakovic is set to play her second round singles against Radwanska, who she beat in the first round at Wimbledon two weeks ago.
The Kiwi has a current WTA singles ranking of 50. Radwanska is 57th.