Veteran Lleyton Hewitt has safely advanced to the second round of the US Open, but Australian young gun Thanasi Kokkinakis is out after succumbing to the brutal conditions in New York.

Hewitt progressed to a potential second-round showdown with Bernard Tomic when Kazakh Aleksandr Nedovyesov quit while trailing Australia’s former world No.1 and 2001 Open champion 6-0 7-6 (7-2) 1-0.

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Kokkinakis threatened to pull off a major upset before having to retire with severe cramping against Wimbledon semi-finalist Richard Gasquet.

The score was locked at two sets apiece – 4-6 6-1 4-6 6-3 – when the 19-year-old was forced to call it a day after dropping serve to trail 2-0 in the deciding set.

Thanasi Kokkinakis reacts to his round one withdrawal after suffering a cramp. Photo: Getty

After seizing a two-sets-to-one lead over the French 12th seed, Kokkinakis dropped eight straight points after serving at 2-2 and 30-love in the fourth set.

He winced in pain as he was treated courtside and could barely move as the punishing heat – which hit 32 degrees – and humidity took hold.

Kokkinakis rolled serves into play at less than 100kmh before being reduced to under-arm serving at one point.

The South Australian looked to the heavens and despairingly told the tennis gods: “It’s absolute torture” before finally stopping after advice from the chair umpire to consider his health.

Shattered by his unfortunate demise, the teenager smashed his racquet into the cement before staggering to the net to shake hands with Gasquet.

Kokkinakis’s sorry departure continues Australia’s disappointing start to the season’s final grand slam event.

Ajla Tomljanovic and qualifier John-Patrick Smith also joined the exodus on Tuesday.

Tomljanovic was unable to convert after taking the opening set in a 6-7 (1-7) 6-2 6-4 first-round loss to Italian Karin Knapp, while Smith also had opportunities in a 6-1 3-6 7-5 7-6 (7-4) defeat at the hands of experienced Russian Mikhail Youzhny.

The trio of losses follow first-round exits on Monday for Casey Dellacqua, Daria Gavrilova, John Millman and Matt Ebden, with Hewitt and Sam Groth Australia’s only winners so far.

Tomic faces Bosnian Damir Dzumhur later on Tuesday before Nick Kyrgios takes on third seed Andy Murray in the feature night match.