Guarnier's teammate Anna van der Breggen played her part setting UP the final assault from the stage winner before finishing second, ahead of Arlenis Sierra (Astana Women’s Team).
Their rivals will try to turn things around with the queen-stage set on Friday.
“It’s really special for me to have a World Tour event here in the US and in California, my adopted home state. My teammates set me perfectly for this win," Guarnier said.
There were several breakaway attempts but nothing stuck with a watchful Boels-Dolmans keeping proceedings in check until van der Breggen split the peloton as the race rolled into Nevada.
Australian Lizzie Williams attacked from the reduced bunch with 40km left to race but that adventurous foray was policed by Boels-Dolmans and the Hagens Berman Supermint rider was soon back in the leading group.
Breaks came and went but Boels-Dolmans maintained control to the base of the final 1.7km climb where Guarnier used van der Breggen as a slingshot for victory.
"Today was quite aggressive, they had a lot of work and let me stay calm and save everything for the finish. It was hectic coming into the final climb," Guarnier said.
"Amy Pieters went super hard, strung things out and opened it up for us. Anna [van der Breggen] went, I followed her and with 300 metres to go it was my time to attack.”