Novak Djokovic charged into a record 47th Grand Slam semi-final on a steamy Tuesday at the US Open with a straight-sets win over Taylor Fritz, while home favourite Coco Gauff stayed on track for her first major title.

Djokovic shrugged off ninth seed Fritz 6-1, 6-4, 6-4 to extend his dominance of American players in New York and take another step closer to a record-extending 24th men's Grand Slam title.

The 36-year-old Serbian star will appear in his 13th US Open semi-final, eclipsing the mark he shared with longtime nemesis Roger Federer for most appearances in the last four of a Grand Slam.

Djokovic awaits the up-and-coming Ben Shelton, who took down 10th seed and 2022 semi-finalist Frances Tiafoe in an all-American affair in Tuesday's night session at Arthur Ashe Stadium.

No luck for Fritz

"I've been playing on this court for many years, so many epic matches and I cannot wait for another one in a few days' time," said Djokovic, a three-time US Open champion.

Djokovic defeated Fritz for the eighth time in a row, weathering stifling conditions as the temperature topped 90 degrees Fahrenheit (32 Celsius) and humidity rose above 55%.

"It was very humid conditions. Difficult to play but that is why we train and try to get ourselves in the best conditions to deliver. Not easy but you have to fight," said Djokovic.

Fritz had lost serve just once across four three-set wins in reaching his first US Open quarter-final, but the 25-year-old was broken three straight times to start the match.

Djokovic resisted four break points at 2-1 in the second set and hauled himself over the line after a rollercoaster final few games in the third set, maintaining his quest for a triumphant return to world number one next week.

The unseeded Shelton unleashed 50 winners, using his booming service and blistering forehand to devastating effect to beat Tiafoe 6-2, 3-6, 7-6 (9/7), 6-2.

Shelton, who reached the quarter-finals on his Australian Open debut in January, is through to the last four of a major for the first time.

He becomes the youngest American men's semi-finalist in New York since 1992.

History made

Shelton, 20, saved a set point as he won a crucial third-set tie-break and pulled away in the fourth to settle a historic first Grand Slam quarter-final in the Open era featuring two African-American men.

"It doesn't get much better than that," world number 47 Shelton said of a first-time meeting with Djokovic scheduled for Friday.

"I feel like I left it all out here tonight. It was an emotional battle.”

"End of that third set is when I really had to dig deep," said Shelton.

"I think that was the key for me tonight. Just being tough and being relentless, and knowing that I could go the distance physically no matter how bad it hurt.”

Tiafoe regretted giving Shelton too many chances to stay in the match.

"Leave door open for a lot of guys, you're playing with fire," he said. "Just gonna learn from these moments... It hurts now."

Gauff cools off Ostapenko

Gauff swept into the last four earlier on Tuesday with a 6-0, 6-2 win over Latvia's Jelena Ostapenko in 68 minutes in the baking midday heat.

The 19-year-old is the first American teenager to reach the US Open semi-finals since Serena Williams in 2001.

The sixth seed will meet this year's French Open runner-up Karolina Muchova for a place in Saturday's final in a repeat of the championship match won by Gauff last month in Cincinnati.

"It feels great, I'm so happy," said Gauff. "Last year I lost in the quarter-finals stage and wanted to do better this year. I have a long way to go but I'm happy and will be ready for the next one.”

Gauff has now won 16 of 17 matches since her first round loss at Wimbledon, her recent titles in Washington and Cincinnati establishing herself as one of the US Open favourites.

"There's still a lot of tennis left to play, and it's a long match and a long tournament," said Gauff.

"You know, even though the semi-finals, by theory, if you want to win there's two matches left. You can't think like that.”

Muchova reached her second Grand Slam semi-final of the season with a 6-0, 6-3 demolition of veteran Romanian 30th seed Sorana Cirstea.

The 10th-seeded Czech broke six times and hit 32 winners in a consummate performance.

"I'm just trying to keep things actually pretty easy and don't put much expectations on me," said Muchova.

Cirstea, 33, had been playing in the quarter-finals of a Grand Slam for only the second time in a professional career that began in 2006.

AFP