CoCo Vandeweghe swept past world No 1 Karolina Pliskova to continue the US dominance of the final major of the year in New York
Vandeweghe held her nerve on her second match point to book a semi-final meeting with compatriot Madison Keys, the 15th seed, who beat Estonian qualifier Kaia Kanepi in the first match of the night session.
It means the US has all four ladies semi-finalists in a Grand Slam for the first time since 1985 and in the the last four at Flushing Meadows for the first time since 1981.
Vandeweghe had earlier joined compatriots Venus Williams and Sloane Stephens in the last four, reaching her second Grand Slam semi-final of the year with a 7-6(4) 6-3 success after reaching the same stage at the Australian Open in January.
The defeat for Pliskova, who was a runner-up in New York last year, means that Garbine Muguruza will become the new WTA world No 1 after the conclusion of the tournament - the Czech needed to reach the final at Flushing Meadows to retain her position at the top of the standings.
"When I won this event as a junior I always dreamed about being here on the real stage," said 25-year-old Vandeweghe.
"To come together this year, it is a process. I did expect it overnight when I was 16 but now here I am and I couldn't wish for anything better.
"I watched the match last night with Venus and think she said it best. We have to admire Serena and Venus, Lindsay (Davenport), Jennifer (Capriati). They all motivated me to be the next great American coming up and let's make it four for
four."
Vandeweghe, coached by former Wimbledon champion Pat Cash, enjoyed the faster start claiming the first break of the match in the third game but Pliskova recovered the break deficit to level the opener at 4-4 after a game which included back-to-back double faults from the American.
Both players then held serve despite the American facing pressure from the top seed Pliskova only for the 20th seed to clinch the first set in a tie-break with some strong serving under pressure.
Vandeweghe secured a key break of serve in the fourth game of the second set but immediately gave the advantage back to her opponent after Pliskova secured the break back on her third opportunity of the game.
However, the home favourite responded immediately for a third successive break of the set to regain command of the set to move 4-2 ahead before holding serve to move within one game of claiming victory.
Pliskova then eased through a service hold to put the pressure on the American's shoulders but after a tense game she delighted the Arthur Ashe Stadium to make it three from three for the US before Keys completed the set under the floodlights.
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