Johanna Konta brushed aside 23-time Grand Slam winner Serena Williams 6-1 6-0 in San Jose.
Konta, ranked 48th in the world, took less than an hour to hand Serena the worst defeat of her career, and book her place in the second round of the Silicon Valley Classic.
Her 53-minute rout of the younger Williams sister started with two games going to serve before the Briton won five on the bounce.
The second set was even more clinical than the first, as Konta won two service games to love and dished out the bagel on the first of two break – and match – points.
It was the most one-sided loss of Williams’ career, in which she served seven double faults and made 25 unforced errors compared to Konta’s nine.
The Briton will go on to play Sofia Kenin in the next round.