Kevin Anderson defeated Sam Querrey to become the first South African to reach the semi-finals of a grand slam for 14 years.
The 31-year-old came out on top of a predictably tight encounter that finished just before 2am at Flushing Meadows, with Anderson winning 7-6 (7/5) 6-7 (9/11) 6-3 7-6 (9/7).
Not since Wayne Ferreira at the 2003 Australian Open has a South African made the last four at a slam, while Cliff Drysdale in 1965 was the last man to do so in New York, when the tournament was still amateur.
Anderson made his first grand slam quarter-final at the US Open two years ago but has been hampered by injuries since, dropping as low as 80 in the rankings in January.
He said: “This is incredible. Playing on this stage, one of the most famous courts in the world in a night session, getting through feels absolutely fantastic.”
In one of the most unlikely slam semi-finals of recent years, Anderson will take on Spain's Pablo Carreno Busta for a place in the title decider.
Anderson was keen to savour his achievement before focusing on that challenge, saying: “This is very special for me, I’m going to try to enjoy it a little bit. It’s going to be a tough battle but I’m just so excited to be competing in a semi-final of a grand slam.”
With the players boasting a combined height of 13 feet and two inches, this was the tallest match this late at a grand slam in the Open era.
Both giants knew what a huge opportunity it was to reach a slam semi-final and very possibly a final.
Querrey’s form in blitzing Mischa Zverev in the fourth round suggested the American was the favourite on his home stage but it was always likely to be a close contest.
They had met 14 times before, with Querrey winning eight, including a five-setter at Wimbledon this summer on his way to the last four, but Anderson coming out on top of their last match in Montreal last month.
It was the South African who drew first blood, winning the final five points of the first-set tie-break after Querrey had seemed poised to take it.
The clock ticked past midnight as they entered a second tie-break, and Querrey almost let slip an even more dominant position, allowing 6-1 to become 6-6 before finally taking his eighth set point.
But back came Anderson to take the third set and the 28th seed edged the fourth-set tie-break too, converting his second match point when Querrey missed a forehand.
Earlier, Carreno Busta defeated Diego Schwartzman to reach his first grand slam singles semi-final.
The 12th-seeded Spaniard, the highest-ranked player left in the bottom half, proved too solid for his opponent, winning 6-4 6-4 6-2.
It was a closer match than the scoreline suggested but, as in his fourth-round victory over Denis Shapovalov, Carreno Busta played the big points superbly.
There could yet be an all Spanish final, with Rafael Nadal due to face Andrey Rublev in the quarter-finals on Wednesday.
Carreno Busta is well used to being completely overshadowed by his countryman, who has played in 25 slam semi-finals and won 15 titles.
“Of course if you speak with some Spanish people about tennis, everybody knows Rafa,” said the 26-year-old.
“It’s true that Rafa is an incredible tennis player, is one of the best ever. But there are a lot of Spanish players, good Spanish players. And now I am in the semi-finals of the US Open, and I think it’s as important as if Rafa arrives to the semi-finals.
“So maybe it’s just easier when, in your country, Rafa has all the attention and you are very without this pressure.”
