NEW YORK (AFP) - Five-time champion Roger Federer breezed through sweltering conditions at the US Open on Tuesday but the crushing heat and humidity took the number of first-round retirements to a record nine.
Second-seeded Federer had little trouble in seeing off Argentina's world number 34 Leonardo Mayer 6-1, 6-2, 6-2 in just 77 minutes on Arthur Ashe Stadium.
The 34-year-old Swiss, bidding to become the oldest champion in New York in 45 years, fired 12 aces, 29 winners and broke serve six times.
The 17-time Grand Slam champion goes on to face either Marcos Baghdatis or Steve Darcis.
"I got off to a good start and my serve got better as the match went on," said Federer.
However, the day's drama was being served-up on Court Five where Australia's Thanasi Kokkinakis retired on one leg in the fifth set against French 12th seed Richard Gasquet.
The 19-year-old Kokkinakis, who was caught up in compatriot Nick Kyrgios's infamous sex slur against Stan Wawrinka in Montreal, suffered from cramping and was warned by the umpire that he was putting his health at risk if he continued.
But he battled on, serving from a standing start and forced to play at walking pace before he finally gave up, losing 4-6, 6-1, 4-6, 6-3, 2-0 after almost three hours in 30-degree heat.
He was the eighth man to retire from the first round, a record for the US Open before Kazakhstan's Aleksandr Nedovyesov quickly became the ninth.
He was down 6-0, 7-6 (7/2), 1-0 to former champion Lleyton Hewitt when he called a halt after suffering a right shoulder injury.
Earlier, Latvia's Ernests Gulbis also quit, handing Great Britain's Aljaz Bedene a 3-6, 6-4, 3-0 win.
Six men had retired on Monday.
In other early men's action, American number one John Isner breezed past Malek Jaziri of Tunisia 6-2, 6-3, 6-4 on the back of 24 aces and 54 winners.
Czech sixth seed Tomas Berdych, who made the semi-finals in 2012, was also a comfortable winner, seeing off American wildcard Bjorn Fratangelo 6-3, 6-2, 6-4.
Japan may have lost fourth seed Kei Nishikori in the first round on Monday, but 19-year-old Yoshihito Nishioka restored some national pride with a 6-4, 2-6, 6-7 (7/9), 6-1, 6-2 win over fellow qualifier Paul-Henri Mathieu of France.
In the women's draw, Lucie Safarova joined the seeds casualty list when the Czech left-hander became the fourth top-10 player to lose in the first round.
Sixth-seeded Safarova slipped to a 6-4, 6-1 defeat to Ukraine's Lesia Tsurenko, the woman she beat in the semi-finals in New Haven just last week.
Safarova, the French Open runner-up, joins seventh seed Ana Ivanovic, eighth-ranked Karolina Pliskova and Carla Suarez Navarro, the 10th seed, in failing to get out of the first round.
With world number three Maria Sharapova having pulled out of the tournament through injury, Safarova's defeat also served to ease Serena Williams's path to a calendar Grand Slam.
The world number one American reached the second round on Monday when Vitalia Diatchenko retired with a foot injury after just 30 minutes.
World number two Simona Halep avoided the upsets when she reached the second round thanks to New Zealand opponent Marina Erakovic retiring with a knee injury.
Halep was leading 6-2, 3-0 when her 99th-ranked rival called it quits.
Romanian 23-year-old Halep goes on to face Kateryna Bondarenko of Ukraine.
"I had a good start. I was aggressive and played my best tennis today," said Halep, who has yet to get beyond the fourth round in New York.
Fourth-seeded Caroline Wozniacki also avoided the cull of the top seeds by beating American college champion Jamie Loeb, ranked at 413 in the world, 6-2, 6-0.
Wozniacki, the 2009 and 2014 runner-up, will face either Christina McHale of the United States or Petra Cetkovska of the Czech Republic for a place in the last 32.
Two-time runner-up Victoria Azarenka, seeded 20, eased past Lucie Hradecka of the Czech Republic 6-1, 6-2.
In the Tuesday night session, third seed Andy Murray, the 2012 champion, begins his campaign against controversial Australian Nick Kyrgios, the world number 37.
The 20-year-old Australian has lost all three of his matches against Murray.