NEW YORK -- Naomi Osaka pointed two fingers at her temple, her face grim as she looked toward her guest box.
She'd just dropped the second set, moments after wasting a match point, as her US Open title defense got off to a shaky start Tuesday. Her body language told the story: the eye rolls, the balled-up fists covering her face at a changeover, the racket resting atop her head.
Back in Arthur Ashe Stadium, where she beat Serena Williams in last year's chaotic final, the No. 1-seeded Osaka kept digging holes and kept climbing out of them, eventually emerging with a 6-4, 6-7 (5), 6-2 victory over 84th-ranked Anna Blinkova of Russia in the first round.
"I felt nervous; for me, it's definitely a new feeling," Osaka said after her win. "It was consistent throughout the entire match, which was very strange for me. ... It never really went away."
The 21-year-old from Japan wore a black sleeve over her left knee, which has been an issue recently.
But it wasn't so much her movement as her erratic strokes that presented problems for Osaka, who finished with 50 unforced errors. Blinkova had just 22.
"You kind of want to do well after you did well last year," Osaka said, when asked why she felt so many jitters while trailing 3-0 and 4-1 at the outset. "I just definitely didn't want to lose in the first round."
She added later: "I really didn't expect myself to play amazing today."
Only two US Open women's champions have lost in the first round the following year during the professional era: It happened in 2005 to Svetlana Kuznetsova and again in 2017 to Angelique Kerber -- who was beaten by none other than Osaka, ranked 45th at the time and yet to get past the third round at a major tournament.
Osaka thought back to that match Tuesday.
"I could kind of see how stressed out [Kerber] was and that was in my favor,'' Osaka said. ``I don't want to give people that look.''
Tuesday's victory, as difficult as it was, stretched Osaka's winning streak in hard-court Grand Slam matches to 15, which includes her run to the titles at Flushing Meadows in 2018 and at the Australian Open in January.
Those helped her become the first Japanese tennis player to be ranked No. 1, a spot she regained this month.
Osaka has spoken rather openly about the struggles she's had dealing with pressure and expectations this season. She said Tuesday that she hoped figuring out how to get past Blinkova -- who is now 0-2 at the US Open and 0-4 against top-10 opponents -- would boost her moving forward.
"It helps me a lot, because I learn from the tougher matches,'' Osaka said. "It helps me be prepared and try to learn and adjust my game plan.''
The fourth-seeded Halep won 6-3, 3-6, 6-2 on Louis Armstrong Stadium, where the previous year she had fallen to Kaia Kanepi. In 2017, she was beaten by Maria Sharapova in a night match on Arthur Ashe Stadium.
Gibbs, who wasn't able to play much after a form of cancer was found in her mouth during a trip to the dentist in the spring, remained winless on tour this season. She recently returned in an effort to qualify for the US Open, losing in the final round of qualifying but getting into the main draw when another player withdrew.
In other Day 2 results, two-time major champion Garbine Muguruza was eliminated by Alison Riske of the U.S. 2-6, 6-1, 6-3, while two-time Wimbledon winner Petra Kvitova, No. 7 seed Kiki Bertens, No. 13 Belinda Bencic and No. 15 Bianca Vanessa Andreescu all won in straight sets.
No. 4 Simona Halep was stretched to a third set by American Nicole Gibbs before advancing with a 6-3, 3-6, 6-2 win. American Taylor Townsend lost the first set to Kateryna Kozlova, but also reached the second round.
The Associated Press contributed to this report.