Both the top ranked men's and women's seeds have easily advanced to the second round of the US Tennis Open in New York.
The men's number one Novak Djokovic cruised into the second round of the US Open while Japanese fourth seed Kei Nishikori crashed out after his runner-up effort last year.
Women's number one Serena Williams advanced after Russia's Vitalia Diatchenko retired injured.
Williams won the first set 6-0 and was up 2-0 in second when Diatchenko withdrew.
Djokovic needed only one hour and 11 minutes to capture a 6-1 6-1 6-1 victory over Brazil's Joao Souza.
"There's something I love about number one for sure. Hopefully I can keep it up," said Djokovic.
"I'm just hoping I can continue to play this way and if I can, I feel I have a really good chance against anybody."
Djokovic's highest-ranked possible semi-final foe had been Nishikori, but last year's US Open runner-up exited the US Open at the first match for the third time in five years as France's 41st-ranked Benoit Paire saved two match points and defeated the Japanese star 6-4 3-6 4-6 7-6 (8/6) 6-4.
The 26-year-old Paire, having collected his maiden ATP Tour title last month in Bastad, brought his good form to Flushing Meadows, grinding out the victory in just over three hours to get the season's final tennis grand slam off to a shocking start.
Japan's Nishikori, who turned in a marathon effort last year - recording five-set wins over Milos Raonic and Stan Wawrinka and a four-set victory over world number one Novak Djokovic in the semi-finals - had looked ready to survive the opening test, coming back from a wobbly opening set.
But after the 41st-ranked Paire won the tiebreak, he carried the momentum into the fifth set and recorded the decisive break to go up 3-2, before finishing off Nishikori with a thundering ace.
Meanwhile, former world number one Ana Ivanovic was the first major casualty in the women's draw as the Serbian seventh seed fell 6-3 3-6 6-3 to Dominika Cibulkova.
The 50th-ranked Cibulkova of Slovakia seized the advantage with a service break in the fourth game of the third set for a 3-1 lead and consolidated it with a backhand drop shot to make it 4-1 against the former French Open champion.
A backhand long from Ivanovic, who had her left foot taped midway through the final set, ended the nearly two-hour contest.
"Today I know that my game was there on the court," said the 26-year-old Cibulkova, who cracked the top 10 last year before finishing the season ranked 11th and reached the quarter-finals last week in New Haven.
"I just had to stay tough and know I had to do it, she doesn't give away shots."
Cibulkova, a 2014 Australian Open finalist who earlier this year had Achilles-related surgery on her left foot, will next face American qualifier Jessica Pegula, a 7-5 6-3 winner over Belgian Alison Van Uytvanck.
For Ivanovic, the 2008 French Open champion, the result continued an up-and-down season. The 27-year-old Serb, who reached the semi-finals at Roland Garros this year, was coming off back-to-back quarter-finals at U.S. Open tune-up events in Toronto and Cincinnati.
She also has lost three times to players outside the top-100 this year, including twice at grand slams.