NEW YORK — For years and years, a first-round victory by Venus Williams at a major tournament would hardly merit a mention.
She is, after all, a seven-time Grand Slam singles champion. She’s been the runner-up another seven times.
She was ranked No. 1, owns Olympic gold medals, and is second to her younger sister Serena among active women in several key categories, including Grand Slam match wins, with 215.
And yet nowadays, at age 33, two years removed from being diagnosed with an autoimmune disease that saps energy, hampered much of this season by a bad lower back, and her ranking down to 60th, Williams entered Day 1 at the 2013 US Open having won a total of three matches over the past five Grand Slam tournaments. Plus, she was facing 12th-seeded Kirsten Flipkens, who was a semifinalist at Wimbledon last month and beat Williams on a hard court this month.
Looking very much like the player she used to be, Williams smacked serves at up to 120 miles per hour, returned superbly, covered the court well enough to hit a handful of swinging volley winners, and beat Flipkens, 6-1, 6-2, Monday to reach the second round at Flushing Meadows.
Flipkens, for one, was not surprised in the least to see Williams play that way. To Flipkens, this was not an upset — no matter what the rankings indicate.
‘‘If Venus is there — if she’s fit, if she’s focused — she’s a top-10 player,’’ Flipkens said.
Williams, who topped the WTA rankings in 2002, hasn’t cracked the top 10 since she was No. 9 in March 2011. She hasn’t been past the third round at a Grand Slam tournament since a fourth-round exit at Wimbledon later that year.
During the night session, Serena Williams began her title defense with a 6-0, 6-1 victory, a performance so thoroughly impressive that her opponent, 2010 French Open champion Francesca Schiavone, was prompted in a brief moment of levity to seek comfort by hugging a ball boy.
The match lasted exactly an hour, and light rain began falling right after it ended. Eventually, play was called off for the day, postponing Roger Federer’s match against Grega Zemlja until Tuesday.
Rafael Nadal delivered a straightforward, straight-set victory over 21-year-old American Ryan Harrison.
Sloane Stephens, a 20-year-old American seeded 15th, dropped her opening set, then trailed, 4-2, in the third and 3-1 in the closing tiebreaker, before coming back to edge 110th-ranked Mandy Minella, 4-6, 6-3, 7-6 (7-5).