Poland's Iga Swiatek returns the ball to Latvia's Jelena Ostapenko (not in photograph) during the US Open tennis tournament women's singles round of 16 match at the USTA Billie Jean King National Tennis Center in New York City, on Sept 3, 2023. (PHOTO / AFP)

NEW YORK - Iga Swiatek's US Open title defense and reign as world number one came to an end on Sunday with a shock loss to Jelena Ostapenko, while Novak Djokovic continued his march towards a 24th Grand Slam crown.

Swiatek's 3-6 6-3 6-1 fourth-round defeat brought the day to a stunning conclusion but it was not a surprise to some, with Ostapenko extending her domination over the Pole having won all four career meetings.

"I had nothing to lose today," said the 20th seeded Latvian. "I knew she's a great player and she's very, very consistent, especially last few years.

"I also knew she would have all the pressure.

Iga Swiatek's defeat means a new US Open women's champion will be crowned next Saturday, and when the world rankings are updated on Sept 11 it will be Aryna Sabalenka's name at the top of the list

"I was just trying to make it hard for her and to play my game and to fight until the very last point."

Swiatek's defeat means a new US Open women's champion will be crowned next Saturday, and when the world rankings are updated on Sept 11 it will be Aryna Sabalenka's name at the top of the list.

There will be a new men's world number one as well, with Djokovic retaking top spot, but the Serb's primary goal remains a fourth US Open title that would see him match Margaret Court's record haul of 24 Grand Slams.

The 36-year-old took another confident step towards that objective on Sunday, easing past Croatia's Borna Gojo 6-2 7-5 6-4 to reach the Flushing Meadows quarter-finals for the 13th time.

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Jelena Ostapenko, of Latvia, returns to Iga Swiatek (not in photograph), of Poland, during the fourth round of the US Open tennis championships, on Sept 3, 2023, in New York. (PHOTO / AP)

'Exciting time'

Until the late-night Swiatek drama, the day had belonged to local hopes with five US players competing in eight matches on the two steamy show courts.

It has been two decades since Andy Roddick became the last American man to win the US Open, and 2017 since Sloane Stephens hoisted the women's trophy, but as the season's final Grand Slam enters its second week there is a belief both finals next weekend could feature a home grown contender.

For the first time since 2005 there will be three American men in the last eight, with Taylor Fritz, Frances Tiafoe and Ben Shelton all posting last 16 wins.

And there is certain to be at least one US man through to the semi-finals after Tiafoe swatted aside Australian wildcard Rinky Hijikata 6-4 6-1 6-4 and Shelton beat compatriot Tommy Paul 6-4 6-3 4-6 6-4 to set up a last eight all-American clash.

Novak Djokovic, of Serbia, returns to Borna Gojo (not in photograph), of Croatia, during the fourth round of the US Open tennis championships, on Sept 3, 2023, in New York. (PHOTO / AP)

"Ben has wanted to play me at the Open for a long time," said Tiafoe, who electrified the tournament with his run to the semi-finals last year. "So he's going to be super excited. He's going to come out with a lot of energy.

"It's going to be a great atmosphere.

"Two people of colour playing in the quarter-finals, huge match on Arthur Ashe.

"It's a pretty monumental moment."

Fritz, who has not yet dropped a set, advanced with a tidy 7-6(2) 6-4 6-4 win over Swiss qualifier Dominic Stricker.

USA's Taylor Fritz returns the ball to Switzerland's Dominic Stricker (not in photograph) during the US Open tennis tournament men's singles round of 16 match at the USTA Billie Jean King National Tennis Center in New York City, on Sept 3, 2023. (PHOTO / AFP)

His reward? A last eight meeting with Djokovic.

Gauff was the first US woman into the last eight, ending Caroline Wozniacki's return to Flushing Meadows 6-3 3-6 6-1, and was probably preparing for a showdown with Swiatek until Ostapenko rewrote the script.

READ MORE: Gauff outlasts Wozniacki to reach US Open quarter-finals

Top ranked US woman Jessica Pegula, 2017 finalist Madison Keys and Peyton Stearns will all have their opportunity to join Gauff on Monday when they play their fourth-round matches.

"With Ben and Frances winning guarantees a person in the semi," said Gauff. "With Jess (Pegula) and Maddie (Keys) playing, it guarantees a person in the quarters.

"It's just really exciting tennis for America."