Defending champion Naomi Osaka battled from behind to beat Russian 20-year-old Anna Blinkova 6-4 6-7 (5-7) 6-2 in the first round of the US Open.

The world number one was 4-1 down in the opening set before she won five games in a row to take the lead.

In a second set riddled with errors, she saw off three sets points and held match point before losing a tie-break.

Japan's Osaka, who made 50 unforced errors in the match, fought off three more break points in the decider.

The top seed will now face Polish world number 53 Magda Linette in round two.

'It's just a game - I have to remember that'

Osaka, 21, announced herself to the tennis world when she won back-to-back Grand Slams in New York a year ago and Melbourne in January.

That propelled her up the world rankings but Osaka said in June her French Open third-round exit was "probably the best thing that could have happened" because she was suffering headaches from the "stress" of being the top seed.

She was then dumped out of Wimbledon in the first round before retiring with a knee injury in the quarter-finals at Cincinnati this month - the same knee was heavily strapped here at Flushing Meadows.

"I don't think I've ever been this nervous in my life," Osaka told the crowd on Arthur Ashe court. "I came off really slow and never really found my rhythm. I fought as hard as I could and managed to win.

"You want to do well after you did well last year. I didn't smile much playing this match so hopefully I can change that in the next match. It's kind of just a game so I have to remember that."

Osaka avoided becoming only the seventh player to lose in the opening round of a women's singles title defence at a Grand Slam, while defeat would have cost her the number one ranking.

Muguruza out but Kvitova through

There was, however, a first-round exit for former Wimbledon champion Garbine Muguruza, who lost 2-6 6-1 6-3 to Alison Riske.

American Riske, ranked 11 places below the Spaniard at 36th, sealed her first win at Flushing Meadows since 2013.

Meanwhile, two-time Wimbledon champion and sixth seed Petra Kvitova advanced by beating fellow Czech Denisa Allertova 6-2 6-4.

Former French Open champion Jelena Ostapenko, Swiss 13th seed Belinda Bencic and Dutch seventh seed Kiki Bertens are also through.

Latvia's Ostapenko overcame Serb Aleksandra Krunic 6-3 7-6 (7-9), while Bencic beat Luxembourg's Mandy Minella 6-3 6-2. Bertens won 6-4 6-2 against Spaniard Paula Badosa.