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 either 10th seed Frances Tiafoe or the up-and-coming Ben Shelton, who face off in an all-American affair in Tuesday's night session at Arthur Ashe Stadium.

"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.

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.

Sixth seed Gauff will meet this year's French Open runner-up Karolina Muchova for a place in Saturday's final.

"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."

"I didn't feel comfortable at all the whole match, even at match point. She has the ability to come back no matter the scoreline so I was just trying to play every ball and hit it deep."

The 19-year-old Gauff has now won 16 of 17 matches since her first round loss at Wimbledon, picking up titles in Washington and Cincinnati to establish herself as one 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."

An out-of-sorts Ostapenko criticised the tournament scheduling as she returned to court barely 36 hours after bundling out world number one Iga Swiatek in the last 16 late on Sunday.

"I was pretty sure I'm gonna play at night session, because that's what they told me," she said.

"When I saw the schedule I was a little bit surprised, not in a really good way."

Muchova reached her third Grand semi-final 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.

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.