Madison Keys outdueled fellow American Vandeweghe 7-6(4) 6-4 on Sunday to win the Stanford Classic and capture her first title of the year.
In an evenly matched contest between two friendly opponents, third seed Keys was impregnable on serve but claimed the only break in the second set before closing out a confidence-boosting win ahead of the U.S. Open.
Keys missed the opening two months of the season after undergoing surgery on her left wrist but has worked her way back into solid form, knocking out Wimbledon champion Garbine Muguruza in the semi-final.
Vandeweghe, who reached the semi-finals of the Australian Open and the quarter-finals at Wimbledon this season, was also looking for her first title of 2017.
She blasted six aces but faltered in the opening set tie-break to allow Keys to take control.
(Writing by Jahmal Corner; Editing by Ian Ransom)