Portugal Colonial - Battling Gauff nears Swiatek clash, Djokovic eyes US Open last 16

The in-form Gauff, coming off titles in Washington and Cincinnati, had to dig deep to withstand Belgium's Elise Mertens as the 19-year-old American fought her way to a 3-6, 6-3, 6-0 victory.

"A win is a win, it doesn't matter how you get it done," said Gauff. "If anything the three-setters show everybody else I'm not going down without a fight."

Mertens, twice a quarter-finalist in New York, fended off a pair of break points in the sixth game of the first set and then broke twice in succession to surge ahead.

Gauff, taken the distance in the opening round, held off a barrage of break points early in the second set before swinging the momentum in her favour as Mertens began to falter.

She finished off in style by winning 10 games on the bounce to book a fourth-round meeting with Caroline Wozniacki, moving her one win away from a possible blockbuster quarter-final with Swiatek.

The Pole briefly put sentiment to one side as she demolished 145th-ranked Slovenian qualifier and best friend Kaja Juvan 6-0, 6-1 in just 49 minutes to storm into the fourth round.

"I didn't like the fact that I was kind of winning with my best friend," said world number one Swiatek. "It was like playing against a sister because I've known her for so long.

"I don't have many friends but she's my best friend so that was the toughest part for sure."

Swiatek is bidding to become the first woman to successfully defend her US Open crown since Serena Williams won a hat-trick of titles from 2012-2014.

She next faces 2017 French Open champion Jelena Ostapenko, who beat Bernarda Pera in three sets.

Former world number one Wozniacki, playing her first Grand Slam in over three years, kept her fairytale US Open return going with a 4-6, 6-3, 6-1 win over Jennifer Brady.

Czech 10th seed Karolina Muchova qualified for the last 16 courtesy of a 7-6 (7/0), 6-3 win over Taylor Townsend.

She goes on to play China's Wang Xinyu who battled into the fourth round of a Grand Slam for the first time by coming from a set down to oust Slovakia's Anna Karolina Schmiedlova 4-6, 6-3, 6-2.

- Djokovic faces fellow Serb -

Djokovic can take another stride towards a record-extending men's 24th Grand Slam crown when he meets Laslo Djere in an-all Serbian match-up in the night session on Arthur Ashe.

"I'm pleased with the way I'm feeling, playing on the court," said Djokovic, who has dropped only 11 games through the first two rounds.

"Can always be better, but first two rounds didn't spend too much time on the court and played very solid and hopefully I can keep building."

Djere, the 32nd seed, is trying to reach the fourth round of a major for the first time in a career marked by the trauma of losing both of his parents to cancer by the time he was 23.

"He had a lot of struggles with his family and private issues. You know, had to endure all of that," Djokovic said. "It says a lot about his mental resilience."

Ninth seed Taylor Fritz led a quartet of American men through to the fourth round on Friday.

Fritz crushed Czech qualifier Jakub Mensik 6-1, 6-2, 6-0. Mensik was the youngest man to reach the US Open third round since 1990 and celebrated his 18th birthday on Friday.

Frances Tiafoe, a semi-finalist last year, progressed with a 4-6, 6-2, 6-3, 7-6 (8/6) win over unorthodox Frenchman Adrian Mannarino.

"He's so annoying to play," said Tiafoe.

"He's bunting the ball around. It's so slow. You look at him and are like 'What's he doing?' But it's so effective.. he's super tough."

Tommy Paul, the 14th seed, advanced with a four-set win over Spain's Alejandro Davidovich Fokina, while Ben Shelton put out Aslan Karatsev 6-4, 3-6, 6-2, 6-0.

Swiss qualifier Dominic Stricker prolonged his breakout run by outlasting French wild card Benjamin Bonzi 2-6, 7-5, 7-6 (7/4), 3-6, 6-2.

Rinky Hijikata's improbable ride also continued as the Australian wildcard entrant reached the fourth round with a 6-3, 6-3, 4-6, 6-3 win over China's Zhang Zhizhen.

X.Brito--PC