With the temperature once again nudging towards 38C, 19-year-old Gauff warmed up the Arthur Ashe crowd by speeding past Latvia's Jelena Ostapenko 6-0 6-2 to become the youngest American to reach the US Open women's semi-finals since Serena Williams in 2001.

But Fritz could not keep the party going, although the 25-year-old had his opportunities, converting only two of 12 break chances while committing 51 unforced errors, almost double his opponent's 26.

Fritz had lost all seven career meetings with Djokovic and never beaten a top-10 opponent at a Grand Slam but rolled into the quarter-finals in sensational form, the only player to not drop a set and broken only once in 50 service games.

Djokovic wasted no time ending both those runs, breaking the American three times before ending the first set with a booming ace and never took his foot off the gas.

The fickle New York crowd has never really fully embraced Djokovic and the Serb is likely to find himself increasingly unpopular this week.

Not since Andy Roddick in 2003 has an American man won the US Open and Djokovic could single-handedly dash home hopes of ending that drought.

Having eliminated Fritz he now finds 20-year-old Shelton standing between him and a 10th trip to the final.

"It's normal, it's logical to expect that most of the crowd would support the home player," said Djokovic. "That's probably going to be the case on Friday, but I'll be ready for it.

"I'm trying to enjoy the moments on the court, but there is so much stress and pressure going on that it's hard to have fun on the court.

"It's really about finding a way to navigate through the match and win a tennis match for me."

There are not too many sporting events in New York that create more buzz than an all-American clash under the Arthur Ashe Stadium lights at the business end of the season's final Grand Slam.

The atmosphere during a night session is always electric but it was dialed up a few notches for Tiafoe and Shelton, the contest the first in 15 years to feature two Black American men battling on the world's largest tennis venue.

The match lived up to its blockbuster billing as the big-hitting Shelton hammered his way to a 6-2 3-6 7-6(7) 6-2 win, becoming the youngest American to reach the US Open men's last four since Michael Chang in 1992.

If Gauff is to reach her first US Open final she will need to get past tricky Czech Karolina Muchova, who was a 6-0 6-3 winner over Romanian Sorana Cirstea.

The semi-final will be an intriguing match-up between two of tennis's hottest and most creative players.

Since her opening round loss at Wimbledon Gauff has won 17 of her last 18 matches, including titles in Washington and Cincinnati.

Muchova, the French Open finalist, has also been in superb hardcourt form, getting to the round of 16 at the Canadian Open and falling to Iga Swiatek, before losing in the final of the Cincinnati Open to Gauff.

Gauff may not have to carry the US flag into the last four on her own, with Madison Keys, the losing finalist in 2017, meeting Wimbledon champion Marketa Vondrousova on Wednesday in quarter-final action.