NEW YORK (REUTERS) - Naomi Osaka was given a testing workout by Anna Blinkova as she began the defence of her US Open title on Tuesday (Aug 27) but the world No. 1's power and shot-making ultimately proved too much as she prevailed 6-4, 6-7 (5-7), 6-2.

The unseeded Blinkova raced into a 4-1 lead in the first set and a shock appeared to be in the works but Osaka cut down her errors to win five straight games and take the opener.

The tenacious Blinkova refused to back down, however, saving a match point on Osaka's serve in the second before breaking her to set up a tiebreak, which the Russian won when Osaka sent a return into the net.

The 21-year-old Japanese responded by looking to her box and mimicked putting a gun to her head and pulling the trigger.

Osaka stayed composed in the third, however, breaking Blinkova to take a 3-1 lead before sealing the first-round win with a blistering forehand that caught the line. It was an erratic performance for Osaka, who committed an unsightly 50 unforced errors, 28 more than her opponent, but also blasted 44 winners and pounded eight aces.

Osaka said the nerves that come with being a first-time defending champion played a part in her slow start and also gave credit to Blinkova for an impressive performance.

"I don't think I've ever been this nervous in my life," she said in an on-court interview at Arthur Ashe Stadium. "She played really amazing. And for me, I came off really slow. I never really found my rhythm. I fought as hard as I could and I managed to win."

Osaka chose to look on the bright side of her unexpectedly competitive match against the world No. 84.

"It helps me a lot because I learn from the tougher matches. It helps me prepare to have to adjust my gameplan throughout the match."

Next up for Osaka is a second-round meeting with Poland's Magda Linette on Thursday.

Teen sensation Cori "Coco" Gauff lived up to the hype surrounding her US Open debut, battling back to beat Anastasia Potapova 3-6, 6-2, 6-4 in a back-and-forth thriller.

The outlook appeared bleak for the 15-year-old American when she was broken to open the second set but Gauff broke back in the next game to seize the momentum and ultimately level up the contest in front of a supportive crowd.

But hard-hitting 18-year-old Potapova, despite needing medical attention to her shoulder, refused to go down without a fight and Gauff had to earn her place in the second round.

Asked how she turned the match around, wild card Gauff pointed to the fans inside Louis Armstrong Stadium.

"Honestly it's because of the crowd," she said. "You guys were amazing. No matter where I was on the court I could hear somebody supporting me and I'm really grateful for that."

Gauff also had words of praise for her opponent, who battled hard in the third set.

"I was trying to really dig deep. I was like, 'You got to make her play. She's not going to hand it to you," said Gauff. "I really don't remember the match too well because everything is still a blur. But I do remember I think that four-all game, it was just like a lot of battling."

Gauff entered this year's tournament amid high expectations after reaching the last 16 at Wimbledon earlier this year. She next faces 26-year-old Timea Babos of Hungary in the second round at Flushing Meadows.

Three-time champion Rafael Nadal denied John Millman any chance of posting another fairy-tale run in New York as he cruised past the Australian 6-3, 6-2, 6-2.

Millman delivered the upset of the tournament last year when he beat five-time winner Roger Federer in a surprising run to the quarter-finals but he was unable to recreate the same magic against the relentless Spanish second seed.

Nadal said he came on court with a "lot of respect" for Millman.

"He showed last year what he is able to do when he is playing well," he said. "Always at the beginning (of a tournament), the first match everything is a little bit new, even if I have played here plenty of times. The beginnings are not easy.

"To be the first match honestly I think I played a good match, hitting good backhands, some more mistakes maybe with the forehand than usual but generally happy with how I started."

Up next for Nadal will be Australian wildcard Thanasi Kokkinakis.