Add Denis Istomin's name to the already lengthy list of those unfit to continue during the 2015 US Open after he retired from his second-round match against Dominic Thiem on Thursday.
Earlier Thursday, American Jack Sock fainted a third of the way through the fourth set of a second-round match against Ruben Bemelmans. The 28th-ranked Sock was up two sets to one, poised to advance to the third round and face Stan Wawrinka.
Instead, Bemelmans will be the heavy underdog against the fifth-ranked French Open champion.
Related - Record number of men's players retire in Round 1 of US Open
Like Sock, Istomin will leave Flushing Meadows wondering if he was ill-prepared for the record temperatures and humidity.
Even if he had been fit to continue, the lanky Uzbekistani likely would have lost his second-round match to Austrian youngster Thiem, who's ranked No. 20.