NEW YORK (AP) -- Even before Serena Williams set foot in Arthur Ashe Stadium on Monday night, her path through the U.S. Open to complete a true Grand Slam became a lot easier thanks to losses by other top women.
And when it was the No. 1-seeded American's turn to play her first-round match, she was not tested one bit by a woman who appeared overwhelmed by the opponent, the occasion and, to make matters worse, an injured left foot.
So Williams moved a step closer to tennis' first calendar-year Grand Slam since 1988 without much of a workout, reaching the second round when 86th-ranked Vitalia Diatchenko of Russia stopped playing while behind 6-0, 2-0. Williams was out there for only 27 minutes and took 32 of the 37 points that were played.
"It was definitely different and bizarre," Williams said. "But at the same time, I was still focused. I kept thinking: Just stay focused; don't lose it. You never know what can happen."\
The 33-year-old American told the crowd she appreciates the support she is receiving "on this journey and this milestone that I'm trying to take one match at a time."
Diatchenko, who wore a walking boot to her news conference, said she hurt herself running sprints before the match and that she felt "sharp pain" chasing a backhand during a point. When she was drawn to face Williams, Diatchenko was happy to finally get a chance to meet a player she grew up admiring, but the experience turned out to be "terrible."
"So painful, every step," Diatchenko said.
Next up for Williams is Kiki Bertens of the Netherlands, who is ranked 110th, only once made it as far as the fourth round at a major, and picked up just the second U.S. Open match victory of her career by eliminating Mirjana Lucic-Baroni 3-6, 6-4, 6-2 Monday. Bertens and Williams have never played each other.
Williams is 22-0 in Grand Slam matches in 2015, with championships at the Australian Open in January, the French Open in June, and Wimbledon in July. If she adds the title at Flushing Meadows, she would be the first player since Steffi Graf 27 years ago to win all four Grand Slam tournaments in a season.
Williams also can equal Graf's professional-era record of 22 Grand Slam singles titles - Margaret Court is the all-time leader with 24 - and can become the first woman since Chris Evert in the 1970s to win four consecutive U.S. Opens.
As good as Williams has been, it doesn't hurt to face less-challenging opposition, and several who might have offered a test are gone. On her half of the draw, four top-10 seeds were gone by the end of Day 1: No. 3 Maria Sharapova pulled out Sunday with an injured right leg, and No. 7 Ana Ivanovic, No. 8 Karolina Pliskova and No. 10 Carla Suarez Navarro lost Monday.
Three other seeded women in Williams' side of the bracket departed. No. 29 Sloane Stephens, who beat Williams at the 2013 Australian Open and was a potential third-round opponent in New York, lost to CoCo Vandeweghe 6-4, 6-3. No. 30 Svetlana Kuznetsova, a two-time major champion, and No. 21 Jelena Jankovic, who lost to Williams in the 2008 U.S. Open final, were beaten, too.
"I'm not a person that usually looks at the draws," Williams said. "I just take it as it comes and as it goes."
If Williams defeats Bertens, she would face the winner of an all-U.S. matchup between Wimbledon quarterfinalist Vandeweghe - whose uncle Kiki is a former NBA player and now a league executive - and wild-card entry Bethanie Mattek-Sands.
"I don't look ahead. I just look at the next opponent," Vandeweghe said when asked about a possible showdown against Williams. "If you don't get by your next opponent, you have no chance of making a third round."
The only real surprise in men's action was 2014 runner-up Kei Nishikori's 6-4, 3-6, 4-6, 7-6 (6), 6-4 loss to Benoit Paire, who never before had beaten someone ranked in the top five.
It's the first time since 1999 that a man who played in the previous year's U.S. Open final exited in the first round.
The fourth-seeded Nishikori withdrew from a hard-court tournament at Cincinnati in August, citing a hip injury, but said Monday he felt OK physically. Still, he wilted in the 3-hour, 14-minute match on a muggy day when the temperature topped 90 degrees.
The man who beat Nishikori for last year's U.S. Open title, Marin Cilic, won in straight sets, as did No. 1 Novak Djokovic. Two-time U.S. Open champion Rafael Nadal, who missed last year's tournament with a right wrist injury, beat 18-year-old Borna Coric 6-3, 6-2, 4-6, 6-4 in Monday's last match.
"Very happy to be back," Nadal said, "and to be through."