Serena Williams overwhelmed Maria Sharapova 6-1, 6-1 on Monday to reach the second round of the US Open in search of her 24th Grand Slam title while "rusty" Roger Federer rallied past Indian qualifier Sumit Nagal.
Six-time US Open champion Williams crushed the five-time major winner from Russia in only 59 minutes, beating Sharapova for the 19th consecutive time and improving to 20-2 in their all-time rivalry.
"Whenever I play her I bring out some of my best tennis," Williams said. "When you play her you have to be super focused."
Williams, who next plays 121st-ranked US wildcard Caty McNally, blasted five aces and 16 winners while Sharapova made 20 unforced errors.
"She served really well. Found her spots really well," Sharapova said. "I think that's where she hurt me a lot."
Williams is hoping to match the all-time record of 24 Slam singles titles won by Margaret Court.
Swiss third seed Federer, who has a men's record 20 Slam titles, dropped the opening set in 36 minutes, then returned to form and defeated Nagal 4-6, 6-1, 6-2, 6-4.
"I played like my beard today. I was rusty," Federer said.
The shock first set was a wake-up call, a 38-year-old legend who was 61-0 in Grand Slam first rounds since the 2003 French Open trailing a 22-year-old from New Delhi who is ranked 190th and fell to 0-5 in tour-level matches.
"Just tried to forget it, play tough, stay with him. It was a tough first set for me," Federer said. "He came back and played really strong. I was missing a lot of balls and trying to cut back on unforced errors.
"It all came back just in time."
Sharapova, the 2006 US Open winner who defeated Williams in the 2004 Wimbledon final, upset Simona Halep in the first round two years ago but could not revive that magic.
The 37-year-old American said that after learning she would face Sharapova, "every practice after that was super focused and super intense."
Eighth-seeded Williams rolled through the first set in 24 minutes then broke to open the second. She denied Sharapova on two break points to hold in the fifth game, an impressive backhand winner ending the threat.
"That was definitely a big point for me," Williams said. "You can't let her get any momentum."
Williams broke again to 4-1, rescued three break points in the sixth game to hold serve and broke again to advance, showing no sign of the back spasms that limited her pre-Open play.
"The body is good," she said. "My back is a lot better. I'm excited. This is going to be fun."
Top-ranked defending champion Novak Djokovic cruised into the second round while French Open champion Ashleigh Barty and third seed Karolina Pliskova struggled but advanced.
Serbian star Djokovic, who has won four of the past five Grand Slam singles titles, dispatched Spain's 76th-ranked Roberto Carballes Baena 6-4, 6-1, 6-4.
"Getting out of the blocks, it takes time for you to feel comfortable on the court," Djokovic said. "I'm quite pleased with my performance and looking forward to the next one."
Djokovic, trying to become the first back-to-back US Open winner since Federer won from 2004-2008, will next face Argentina's 56th-ranked Juan Ignacio Londero.
Djokovic owns 16 Grand Slam titles, four off Federer's record and two back of Spain's Rafael Nadal. Together the "Big Three" have won the past 11 Slam titles and are again heavy favourites.
Australian second seed Barty overcame a horrible start to oust 80th-ranked Zarina Diyas of Kazakhstan 1-6, 6-3, 6-2.
Barty made 19 unforced errors to drop the first set in 28 minutes, but took nine of the last 11 games to book a date with American Lauren Davis.
PliskSerena routs Sharapova in US Open start, 'rusty' Federer wins