New York - Rafael Nadal and Angelique Kerber shrugged off sweltering temperatures to reach the US Open second round on Monday as French Open champion Garbine Muguruza survived a worrying health scare.
Nadal, the 2010 and 2013 champion, took his perfect first round record in New York to 12-0 with a 6-1, 6-4, 6-2 win over Denis Istomin of Uzbekistan.
The Spaniard's reward for a fifth win in five meetings against the Russian-born player is a match-up with Italian veteran Andreas Seppi.
A wrist injury forced Nadal into an early retirement at the French Open and sidelined him from Wimbledon before a gold medal run in the doubles at the Olympics helped ease his misery.
"The most important thing is that I am here in New York. Injuries are part of the career. I had a hard time this year," said the fourth seed.
Kerber needed just over 30 minutes to get her pursuit of a first US Open title off to a winning start.
The second seed and Australian Open champion was leading Polona Hercog 6-0, 1-0 when the Slovenian called it quits, clearly wilting in the 33-degree heat, having won just nine points.
"It's not the way I wanted to win, but I am playing well and feeling good," said the German star.
Kerber, a semi-finalist in 2011, next faces Mirjana Lucic-Baroni of Croatia.
Spanish third seed Muguruza carved out a gritty 2-6, 6-0, 6-3 win over Belgian qualifier Elise Mertens, ranked at 137.
But the French Open champion needed courtside treatment from a doctor after dropping the first set on the Louis Armstrong Court.
The consultation certainly worked as she reeled off the next seven games to lay the foundation for her win.
Muguruza plays Anastasija Sevastova of Latvia for a place in the last 32.
French 13th seed Richard Gasquet, a semi-finalist three years ago, was the day's biggest casualty.
He went down to 6-2, 6-2, 6-3 to British world number 84 Kyle Edmund.
America's John Isner, seeded 20, almost joined Gasquet at the exit before coming back from two sets down to beat 18-year-old compatriot Frances Tiafoe.
Isner, who fired 35 aces, triumphed 3-6, 4-6, 7-6 (7/5), 6-3, 7-6 (7/3) after three and a half hours against the youngest player in the draw.
Croatian seventh seed Marin Cilic, the 2014 champion, eased past Brazil's Rogerio Dutra Silva 6-4, 7-5, 6-1.
Flamboyant French 10th seed Gael Monfils took his summer hard-court record to 15-2 with a 6-4, 6-2, 7-6 win over Gilles Muller of Luxemburg.
Monfils almost suffered a freak accident when a giant courtside clock fell towards him as he collided with the back wall, chasing down a Muller shot.
"When you are in the moment you don't feel really anything. Just jump. I saw a wall, but it was quite lucky," admitted Monfils.
Svetlana Kuznetsova, the 2004 champion, needed only 58 minutes to beat old rival Francesca Schiavone 6-1, 6-2.
The pair famously played the longest women's match of all time at the 2011 Australian Open where Schiavone saved six match points in a four hour 44-minute marathon.
Double Wimbledon champion Petra Kvitova beat Jelena Ostapenko 7-5, 6-3 while former world number one and two-time US Open runner-up Caroline Wozniacki downed US qualifier Taylor Townsend 4-6, 6-3, 6-4.
The Flushing Meadows complex was showcasing its gleaming $600 million refit which includes a retractable roof over Arthur Ashe and a brand new Grandstand court.
However, the old Grandstand court, due to be demolished after the tournament, was pressed into action after Court 10 was deemed unplayable.
Later Monday, world number one and defending champion Novak Djokovic, whose last major ended in a shock third round exit at Wimbledon, starts against Jerzy Janowicz of Poland.
Djokovic, the 2011 and 2015 champion, admits he is "not 100 percent" after suffering a wrist injury on the eve of the Olympics where he was a first-round loser.
Women's top seed Serena Williams and 2012 champion Andy Murray will get underway on Tuesday.
Williams is chasing a record seventh US Open and will equal Steffi Graf's record of 186 successive weeks at world number one.
Results from the first day of the 2016 US Open tennis championships at Flushing Meadows on Monday (x denotes seeded player):
Novak Djokovic (SRB x1) bt Jerzy Janowicz (POL) 6-3, 5-7, 6-2, 6-1
Jiri Vesely (CZE) bt Saketh Myneni (IND) 7-6 (7/5), 4-6, 2-6, 6-2, 7-5
Guido Pella (ARG) bt Bjorn Fratangelo (USA) 6-3, 6-4, 6-4
Mikhail Youzhny (RUS) bt Martin Klizan (SVK x28) 6-2, 6-1, 6-1
John Isner (USA) bt Francis Tiafoe (USA) 3-6, 4-6, 7-6 (7/5), 6-2, 7-6 (7/3)
Steve Darcis (BEL) bt Jordan Thompson (AUS) 5-7, 3-6, 7-6 (7/5), 7-5, 7-5
Ernesto Escobedo (USA) bt Lukas Lacko (SVK) 6-4, 4-6, 4-6, 6-3, retired
Kyle Edmund (GBR) bt Richard Gasquet (FRA x13) 6-2, 6-2, 6-3
James Duckworth (AUS) bt Robin Haase (NED) 4-6, 7-5, 6-3, 4-6, 6-3
Vasek Pospisil (CAN) bt Jozef Kovalk (SVK) 6-1, 6-3, 6-3
Jo-Wilfried Tsonga (FRA x9) bt Guido Andreozzi (ARG) 6-3, 6-4, 6-4
Kevin Anderson (RSA x23) bt Yoshihito Nishioka (JPN) 6-3, 7-5, 6-4
Jack Sock (USA x26) bt Taylor Fritz (USA) 7-6 (7/3), 7-5, 3-6, 1-6, 6-4
Mischa Zverev (GER) bt Pierre-Hugues Herbert (FRA) 6-4, 7-6 (8/6), 4-6, 6-0
Sergiy Stakhovsky (UKR) bt Gastao Elias (POR) 6-1, 3-6, 2-6, 6-3, 7-6 (7/4)
Marin Cilic (CRO x7) bt Rogrio Dutra Silva (BRA) 6-4, 7-5, 6-1
Rafael Nadal (ESP x4) bt Denis Istomin (UZB) 6-1, 6-4, 6-2
Andreas Seppi (ITA) bt Stephane Robert (FRA) 6-2, 3-6, 6-4, 6-3
Andrey Kuznetsov (RUS) bt Thomaz Belluci (BRA) 6-4, 3-6, 6-1, 7-6 (8/6)
Albert Ramos (ESP x31) bt Julien Benneteau (FRA) 3-6, 6-3, 6-3, 2-6, 6-1
Lucas Pouille (FRA x24) bt Mikhail Kukushkin (KAZ) 3-6, 6-2, 6-4, 6-2
Marco Chiudinelli (SUI) bt Guilherme Clezar (BRA) 2-6, 7-6 (8/6), 6-2, 6-4
Federico Del Bonis (ARG) bt Brian Baker (USA) 3-6, 6-7 (6/8), 6-4, 6-2, 6-2
Roberto Bautista Agut (ESP x15) bt Guillermo Garca-Lopez (ESP) 7-5, 6-1, 6-7 (5/7), 7-6 (7/3)
Gael Monfils (FRA x10) bt Gilles Muller (LUX) 6-4, 6-2, 7-6 (7/5)
Jan Satral (CZE) bt Mackenzie McDonald (USA) 4-6, 3-6, 6-3, 6-2, 6-2
Nicolas Almagro (ESP) bt Marton Fucsovics (HUN) 6-1, 6-4, 7-6 (9/7)
Pablo Cuevas (URU x18) bt Dudi Sela (ISR) 6-3, 6-2, 0-6, 5-7, 6-3
Benoit Paire (FRA x32) bt Dusan Lajovic (SRB) 6-2, 2-6, 3-6, 7-5, 6-1
Marcos Baghdatis (CYP) bt Facundo Bagnis (ARG) 6-4, 6-2, 1-1 retired
Ryan Harrison (USA) bt Adrian Mannarino (FRA) 6-4, 7-6 (7/5), 6-3
Milos Raonic (CAN x5) bt Dustin Brown (GER) 7-5, 6-3, 6-4
Kayla Day (USA) bt Madison Brengle (USA) 6-2, 4-2 retired
Duan Ying-Ying (CHN) bt Maria Sakkari (GRE) 6-4, 4-6, 6-3
Naomi Osaka (JPN) bt CoCo Vandeweghe (USA) 6-7 (4/7), 6-3, 6-4
Monica Niculescu (ROM) bt Barbora Zahlavova Strycova (CZE x18) 6-3, 6-7 (3/7), 6-1
Ana Bogdan (ROM) bt Sorana Cirstea (ROM) 0-6, 7-5, 6-2
Caroline Wozniacki (DEN) bt Taylor Townsend (USA) 4-6, 6-3, 6-4
Svetlana Kuznetsova (RUS x9) bt Francesca Schiavone (ITA) 6-1, 6-2
Johanna Konta (GBR x13) bt Bethanie Mattek-Sands (USA) 6-3, 6-3
Tsvetana Pironkova (BUL) bt Virginie Razzano (FRA) 6-1, 6-2
Andrea Petkovic (GER) bt Kristina Kucova (SVK) 7-6 (7/3), 6-3
Belinda Bencic (SUI x24) bt Samantha Crawford (USA) 6-7 (6/8), 6-3, 6-4
Zheng Saisai (CHN) bt Monica Puig (PUR) 6-4, 6-2
Kateryna Bondarenko (UKR) bt Hsieh Su-Wei (TPE) 6-0, 7-5
Anastasija Sevastova (LAT) bt Anna Karolna Schmiedlov (SVK) 6-3, 6-3
Garbine Muguruza (ESP x3) bt Elise Mertens (BEL) 2-6, 6-0, 6-3
Roberta Vinci (ITA x7) bt Anna-Lena Friedsam (GER) 6-2, 6-4
Christina McHale (USA) bt Mona Barthel (GER) 6-2, 6-2
Yulia Putintseva (KAZ) bt Sabine Lisicki (GER) 6-1, 6-2
Carina Witthoeft (GER) bt Misaki Doi (JPN x30) 6-4, 6-1
Lesia Tsurenko (UKR) bt Irina Begu (ROM x21) 6-0, 6-4
Wang Yafan (CHN) bt Alison Van Uytvanck (BEL) 6-3, 7-6 (7/4)
Evgeniya Rodina (RUS) bt Danielle Collins (USA) 6-1, 6-2
Dominika Cibulkova (SVK x12) bt Magda Linette (POL) 6-2, 6-3
Petra Kvitova (CZE x14) bt Jelena Ostapenko (LAT) 7-5, 6-3
Cagla Buyukakcay (TUR) bt Irina Falconi (USA) 6-2, 6-1
Lauren Davis (USA) bt Aliaksandra Sasnovich (BLR) 6-2, 4-6, 7-5
Elina Svitolina (UKR x22) bt Mandy Minella (LUX) 6-7 (5/7), 6-0, 6-2
Shelby Rogers (USA) bt Sara Errani (ITA x27) 6-4, 7-6 (7/3)
Catherine Bellis (USA) bt Viktorija Golubic (SUI) 6-2, 6-3
Mirjana Lucic-Baroni (CRO) bt Alize Cornet (FRA) 6-4, 6-1
Angelique Kerber (GER x2) bt Polona Hercog (SLO) 6-0, 1-0 retired