Kristina Mladenovic stunned 13th seed Ekaterina Makarova at the US Open, to reach her maiden grand slam quarter-final on Sunday.
France's Mladenovic was in the last 16 of a major for the first time, but showed few nerves on her way to an enthralling 7-6 (7-2) 4-6 6-1 win on Arthur Ashe Stadium.
She will next meet fellow unseeded prospect Roberta Vinci, meaning for the third straight year - and for the fourth time in five events - there will be an unseeded semi-finalist in the women's draw at Flushing Meadows.
Mladenovic staved off two break deficits in the opener before prevailing in a tie-break, a fitting end to a tight first set in which the Frenchwoman produced the highlight.
The world number 40 was down a break with Makarova serving at 3-2 15-15, when she produced a brilliant angle-cutting backhand down-the-line winner as the Russian approached the net.
Mladenovic went on to break that game, get broken, and break back again in a whirlwind period, before Makarova was forced to save three set points in the 10th game.
The pair traded some rare easy holds to head to a tie-break which Mladenovic dominated from the outset to claim the first set in one hour.
Neither player blinked on serve throughout the second set until the 10th game, when Makarova earned the first break points of the set via a 0-40 lead - and only needed one to square the match.
Undaunted, Mladenovic - ranked seventh in the world in doubles - showed her quality in the finish, denying last year's semi-finalist with a resounding third-set showing.
Mladenovic conceded only five unforced errors in the decider, and one of her favoured plays in the two-hour, 11-minute contest - the drop shot - helped her set up her 39th winner of the contest to seal progression.
Eugenie Bouchard's withdrawal due to concussion granted Vinci free pass to her third quarter-final appearance at Flushing Meadows in four years.
Vinci, 32, is eyeing her maiden appearance in a major semi-final in what is her 44th main-draw attempt.
Earlier, Venus - the 23rd seed - cruised past qualifier Anett Kontaveit 6-2 6-1, while Serena followed that up with a 6-3 6-3 victory over 19th seed Madison Keys.