World number one Ash Barty has survived a tough examination in her first-round match at the Australian Open, winning in three sets against Ukraine's Lesia Tsurenko.

Key points: Ash Barty dropped the first set 7-5 against Lesia Tsurenko, but only lost two more games before sealing victory

Ash Barty dropped the first set 7-5 against Lesia Tsurenko, but only lost two more games before sealing victory Barty was the only Australia victorious on a rain-marred day one at Melbourne Park

Barty was the only Australia victorious on a rain-marred day one at Melbourne Park Sam Stosur has not reached the second round of the Australian Open since 2015, this year she was beaten 6-1, 6-4 by American qualifier Caty McNally

Barty, fresh from her victory in the Adelaide International on the weekend, lost the first set to Tsurenko before fighting back to triumph 5-7, 6-1, 6-1 on Rod Laver Arena to give Australia its only win on a rain-interrupted day one at Melbourne Park.

Meanwhile, Sam Stosur kept up her annual tradition of first-round exits at the Australian Open, being knocked out in her opening match at Melbourne Park for the fifth straight year.

And men's defending champion Novak Djokovic took four sets to beat German Jan-Lennard Struff 7-6 (7-5), 6-2, 2-6, 6-1, while sixth seed Stefanos Tsitsipas won handsomely against Italian Salvatore Caruso 6-0, 6-2, 6-3.

Tsurenko was never going to be a pushover for Barty, given she was ranked as high as 23 last February before slipping down the rankings when her season was curtailed by an elbow injury in the build-up to the US Open.

The 30-year-old's lack of match fitness told late in the encounter, although Barty was a deserved winner after weathering the early storm from her plucky opponent.

"I think in the first set it was still in my control," Barty said in her courtside interview.

"It was just a little bit of execution. I was just rushing a little bit, trying to finish off points too early.

"Once I was able to get my physicality into it, I felt a lot more comfortable."

Melbourne's rain had left nine matches suspended on the opening day of the tournament and the inclement weather meant Barty and Tsurenko were to face off under the Rod Laver Arena roof.

It is not the first time Barty has arrived at Melbourne Park as the local hope in the women's draw, but it was her maiden appearance at the season-opening major wearing the mantle of world number one.

She looked relaxed when she walked on court but the home crowd was left shocked when the Australian was broken on serve in the opening game of the match.

Tsurenko consolidated the break of serve by holding her own in the second game, before Barty opened her account to trail 1-2.

The contest was back on serve when Barty broke the Ukrainian as her shot selection came to fore and she moved 3-2 ahead by serving to love, an ace out wide icing the fifth game.

But as Barty's tactical nous began to shine through, Tsurenko proved equally adept at dictating play and after holding her serve she broke Barty for a second time, with a brilliantly set-up forehand volley at the net among the game's highlights.

Barty responded by claiming her second service break and then held to lead 5-4, but Tsurenko rallied to win the next three games to secure the opening set in 44 minutes.

Ash Barty dropped her first set at her home major. ( AAP: Michael Dodge )

The Australian had been visibly frustrated when Tsurenko wrested control of proceedings in the first set, but importantly for her legion of fans she did not allow panic to creep into her game in the early stages of the second.

She quickly assumed a 3-0 lead and a second service break gave her a 5-1 advantage later in the set, which she promptly served out in the following game.

Barty again flew out of the blocks in the third and deciding set to snare a double break and lead 4-0. Tsurenko avoided a 'bagel' by holding serve in the fifth game, but Barty powered on to complete her win in one hour and 36 minutes.

She said she had trouble containing her excitement about her return to Rod Laver Arena, this time as the top-ranked player in the women's game.

"I couldn't wait to walk out here on this beautiful court in front of so many people that give me such love and support," Barty said.

"It's incredible."

Stosur exits early again

Stosur acknowledged years ago that she struggles in front of home crowds, and she has not reached the second round of the singles since 2015, with her career-best fourth-round finishes coming in 2006 and 2010.

This time the world number 99 fell to 116th-ranked American qualifier Caty McNally 6-1, 6-4.

Broken in the first game of the match, Stosur quickly found herself down 0-2 before holding serve and powering to 0-40 in the next game. But she squandered all three break points to go behind 3-1.

Sam Stosur struggling at the Australian Open is not a new phenomenon. ( AP: Andy Wong )

Things became more painful on serve in the next game, when she thought she had won it with a backhand at 40-30, only for it to be called long. Five deuces later, she double faulted and McNally broke again.

The American held serve and broke Stosur for a third time to finish off an unfortunately familiar first set for Stosur — aside from being broken three times, Stosur failed to convert all six of her break-point chances in the set, hit 19 unforced errors and two doubles faults.

The second set followed the same pattern, with McNally jumping out to a 3-0 lead before Stosur found her fight to see off two break points and get on the board at 3-1.

The Melbourne Arena crowd rallied behind the Queenslander as she came within millimetres of breaking McNally's serve in the next game, only for the American to eventually hold serve after six deuces.

But Stosur refused to go quietly into that good night and held a tight service game before breaking McNally for the first time in the match and holding serve again to level the set at 4-4.

That was the end of Stosur's resistance, though, as McNally rattled off the next two games to complete the straight-sets win.