Greece’s Maria Sakkari delivered one of the biggest upsets of her career at the WTA San Jose tournament on Friday, ousting former seven-time Grand Slam champion Venus Williams in a straight sets shocker.

The 23-year-old Sakkari saved two set points in the second set en route to a 6-4, 7-6 (7/2) victory over the former world number one, punching her ticket to the semi-finals where she will face another unseeded player, Danielle Collins.

World No.49 Sakkari needed one hour and 43 minutes to dispatch Williams as she has rolled through her first three matches at this event without dropping a set.

Sakkari converted six of her eight break points in the match, and hammered 21 winners, three more than the 38-year-old Williams.

“I was ready for the match, compared to the last times I played against her. I was ready for a battle and ready to play against Venus Williams,” said Sakkari.

Williams, who has won this event twice in 2000 and 2002, made a whopping 43 unforced errors.

Venus’ defeat follows the shocking upset three days ago of her sister Serena, who suffered the most lopsided loss of her career, 6-1, 6-0 to Johanna Konta in round one.

Between the two of them, the Williams sisters committed 68 unforced errors in their elimination games.

Clollins enters semis after Azarenka victory

American Collins moved into the semi-finals after her opponent, former World No.1 Victoria Azarenka, retired midway through the second set due to a back injury.

Sakkari’s mother Angeliki Kanellopoulou was also a top 50 ranked WTA player back in the late 1980s.

Fourth-seeded Elise Mertens ended the giant-killing run of Konta to set up the other semi-final clash with fifth-seeded Mihaela Buzarnescu.

Belgium’s Mertens emerged from a tight match with a 7-6 (7/4), 6-3 victory over Konta.

Mertens broke Konta at love when she served for the opening set, and saved two set points before forcing the tiebreaker.

After dropping her serve in the opening game of the second, Mertens won four games in a row and wouldn’t trail again.

“I just played point-by-point, because anything can happen,” Mertens said. “I believed in myself because it was just one break and I was really happy that I took the first set.”

Mertens reached the semi-finals of the Australian Open in January, but she and Romania’s Buzarnescu will both be battling to reach a first premier level final.

Buzarnescu, who beat Australia’s Ajla Tomljanovic 6-1, 7-5, fell to Mertens in the final in Hobart in January.