For Djokovic, it was another feather on his illustrious cap, as he reached the 47th Grand Slam semi-final of his career, breaking Swiss great Roger Federer's record.

The 23-time Grand Slam champion secured qualification with a 6-1, 6-4, 6-4 win over Fritz, who could not take advantage of the multiple break points he created.

To put them in numbers, the American was successful in only two out of 12 compared to Djokovic emerging on top six times out of nine.

"I just feel that there is always, I guess, an extra gear that you have inside of you and you can find when you dig deep to handle and manage energy levels on and off the court," Djokovic said.

"If you're really devoted to that and if you care about it, if you pay attention to that mental aspect as much as physical, of course."

The Serbian will face Ben Shelton next, who shocked compatriot Frances Tiafoe in an all-American game.

The 20-year-old Shelton, who reached the quarters in the Australian Open this year, saved a set point in the third set tie break to beat Tiafoe 6-2, 3-6, 7-6, 6-2.

Meanwhile, Gauff continued her stellar run on home turf, shocking Jelena Ostapenko of Lativia 6-0, 6-2.

Ostapenko, who knocked out Polish superstar and defending champion Iga Świątek, had a night to forget with 36 unforced errors.

Gauff scripted history by emulating the legendary Serena Williams and becoming the first American teenager to reach the US Open semi-finals since 2001.

"Being in any sentence with her is great," Gauff said.

"She's the greatest player of all time.

"I'm nothing close to that yet, but I’m just honoured to be in the same sentence."

Karolína Muchová will be the next challenge for Gauff, after the Czech Republic star beat Sorana Cîrstea of Romania 6-0, 6-3.

The doubles action saw two-time defending US Open champions Rajeev Ram of the United States and Joe Salisbury of Britain on course for their hat-trick after straight-sets win against Argentines Maximo Gonzalez and Andres Molteni.  

A 6-4, 6-3 win extend their US Open winning streak to 16 matches, setting up a semi-finals fixture against Ivan Dodig and Austin Krajicek.

Croatian Dodig and American Krajicek came out on top against number nine seeds and French-Monégasque player Hugo Nys and partner Jan Zieliński of Poland 6-4, 2-6, 6-3.

The French duo Nicolas Mahut and Pierre-Hugues Herbert will take on Rohan Bopanna of India and Matthew Ebden of Australia in the other men's doubles semi-final.

Herbert and Mahut defeated American Robert Galloway and Italy's Albano Olivetti, 7-5, 6-4, while Bopanna and Ebden dumped out Americans Jackson Withrow and Nathaniel Lammons 7-6(10), 6-1.

In the women's doubles, Jennifer Brady of the United States paired up with Brazilian Luisa Stefani to beat Bernarda Pera and Magda Linette of Poland 7-6, 3-6, 6-3.

Finally, the other quarter-final in the women's doubles saw Canadian Leylah Fernandez and American Taylor Townsend go down to Gabriela Dabrowski of Canda and Erin Routliffe of New Zealand.

Dabrowski and Routliffe upset the number six seeds 2-6, 6-3, 7-6.