"I'm aware what I'm doing, it's unbelievably challenging to play at the highest level as I am now.
And yeah, some days it's harder than others," Murray said.
Isner, 38, won the longest professional tennis match in history against Frenchman Nicolas Mahut at Wimbledon in 2010, which lasted 11 hours and 5 minutes and took place over three days.
The third seed has played second fiddle to Alcaraz and 23-time Grand Slam winner Novak Djokovic at Flushing Meadows but put the field on notice with a first-round demolition of Attila Balazs.
Reporting by Amy Tennery in New York; Editing by Ken Ferris and Ed OsmondOur Standards: The Thomson Reuters Trust Principles.
Persons:
Andy Murray, Bulgaria's Grigor Dimitrov, Brendan Mcdermid, John Isner, Aryna Sabalenka, Briton Murray, Grigor Dimitrov, Arthur Ashe, Murray, Isner, Frenchman Nicolas Mahut, Michael Mmoh, Jack Sock, Jodie Burrage, France's Clara Burel, Carlos Alcaraz, Lloyd Harris of, Alcaraz, Jessica Pegula, Romanian Patricia Maria Tig, Ashe, Sloane Stephens, Russian Daniil Medvedev, Louis Armstrong, Australian Christopher O'Connell, Novak, Attila Balazs, Amy Tennery, Ken Ferris, Ed Osmond
Organizations:
U.S, Wimbledon, New, Australian, Flushing, Thomson
Locations:
Flushing Meadows , New York, United States, Belarusian, Flushing Meadows, Lloyd Harris of South Africa, Romanian, New York, Russian