|Australian Open 2017|
|Venue: Melbourne Park, Melbourne Dates: 16-29 Jan|
|Coverage: Live commentary every day on BBC Radio 5 live sports extra plus TV highlights on BBC Two from 21 January; live text on selected matches on the BBC Sport website.|
World number one Angelique Kerber started the defence of her Australian Open title with a tense 6-2 5-7 6-2 win over Lesia Tsurenko on Rod Laver Arena.
The German top seed was in control at 4-2 up in the second set but two breaks for Tsurenko took it to a decider.
World number four Simona Halep, who needed medical attention on a knee injury, was the first big seed to fall, beaten 6-3 6-1 by Shelby Rogers.
Venus Williams, the 2003 runner-up, beat Kateryna Kozlova 7-6 (7-5) 7-5.
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Kerber labours to victory
Kerber, who saved a match point in round one on her way to the title last year, blew her first match point against Tsurenko as she made hard work of finishing off what had looked to be a straightforward victory.
The 28-year-old had been 5-3 up in the second set but lost the next three games and saved four set points before succumbing on the fifth in a 12th game that lasted almost 10 minutes.
The opening four games of the decider went with serve before Kerber broke Tsurenko's resolve in game five and then broke again in game seven before holding serve to love to wrap up victory.
"I'm really happy to be back here," she said. "Everything started here for me when I won my first Grand Slam here.
"I won the match and that's what counts. The first round is always tough. I'm so happy to be in the second round."
Halep needs time to recover
Halep said she had been battling her knee problem since the WTA Tour Finals in October.
The 25-year-old had no issues during the off-season but it flared up again in Shenzen two weeks ago.
"I can play about 45, 50 minutes without pain. And then it comes," said Halep. "Today it was about 5-3 in the first set, so then it was tough to fight and I couldn't do what I wanted.
"I didn't see the doctor yet. I need an MRI. I probably need some time off to get it recovered, because it's difficult to play with the pain."
American Rogers, beaten in the first round in her only previous Australian Open appearance in 2015, will face the winner of the match between Australia's Ashleigh Barty and Germany's Annika Beck in round two.
"It's pretty incredible, I played really well," said the world number 52.
Veteran Williams seeking rhythm
The 36-year-old Williams played her first Australian Open in 1998 and turned professional in 1994, the year her opponent was born.
The seven-time Grand Slam champion's preparations were hindered by an arm injury.
"It's never easy playing the first round," said the American 13th seed who made 48 unforced errors. "I was just trying to find my rhythm. She didn't make it easy so I'm happy to be through."
Williams next faces either Swiss qualifier Stefanie Voegele or Japan's Kurumi Nara.
Muguruza battles through
French Open champion Garbine Muguruza needed a medical time-out after the first set for what appeared to be a foot problem but the Spaniard recovered to beat New Zealand's Marina Erakovic 7-5 6-4.
"It was very tough when you're playing and starting to feel pain," said seventh seed Muguruza, who will face American Samantha Crawford in the second round.
Elsewhere, Olympic champion Monica Puig was a dominant 6-0 6-1 winner over Patricia Tig, while Jelena Jankovic, who is playing in her 53rd consecutive Grand Slam, beat Laura Siegemund 6-1 1-6 6-4.
Russia's Svetlana Kuznetsova, ranked eighth, completed a tidy 6-0 6-1 victory over Colombian Mariana Duque.
Australian teenager Destanee Aiava became the first player born in this millennium to play a main draw match at a major, but the 16-year-old lost 6-3 7-6 (7-4) to German qualifier Mona Barthel.