Rafael Nadal, Nick Kyrgios and Simona Halep move into Australian Open third round

Pliskova also extends her fine form, while Zverev seems to have rediscovered his game after a miserable ATP Cup

Rafael Nadal was a straight sets winner over Federico Delbonis in the Australian Open second round. Getty Images

On another day at the Australian Open where the biggest players kept their title hopes alive, men's top seed Rafael Nadal and local hope Nick Kyrgios safely reached the third round, while Simona Halep and Karolina Pliskova progressed on the women's side.

Kyrgios looked to be cruising against Gilles Simon when he led by two sets and a break, only for lapses in concentration to allow the Frenchman back into the match, before the Australian world No 26 sealed a 6-2, 6-4, 4-6, 7-5 win inside a pumped-up Melbourne Arena.

Nadal, a 6-3, 7-6, 6-1 winner over Argentina's Federico Delbonis, miscued a shot that hit a ballgirl in the head, but he melted hearts when he apologised and gave her a kiss on the cheek.

"I was so scared for her, honestly," the 19-time Grand Slam winner said. "The ball was quick and straight on the head. She's a very brave girl."

Kyrgios, increasingly popular with home fans after his fundraising efforts for Australia's bushfire crisis, admitted he almost went into a "dark place" when he lost his composure against Simon, but regrouped to win.

"I definitely lost my way a little bit ... but I decided to refocus," Kyrgios said of his mini-meltdown in the third set. "I could have gone to a very dark place in the fourth set but I put it away."

Kyrgios and Nadal stay on course for a fourth-round clash and the next installment in their grudge match after the Aussie hit back at criticism from the "super salty" Spaniard last year.

Their victories followed a day of upheaval caused by the dirty rain, the latest weather problem at a tournament which has contended with bushfire smoke, heavy downpours and strong wind.

As action resumed Alexander Zverev showed signs of a return to form as he downed Egor Gerasimov 7-6, 6-4, 7-5.

The seventh seed has been practising up to seven hours a day after a winless ATP Cup and the hard work paid off as he safely reached the third round.

"Definitely much better than the ATP Cup. Now in the third round, I'm very happy about that," said the 22-year-old German, who beat Italy's Marco Cecchinato in round one.

However, fifth seed Dominic Thiem had a scare as he was taken to five sets by Australia's 140th-ranked Alex Bolt before recovering his composure to win 6-2, 5-7, 6-7, 6-1, 6-2.

"It was all of a sudden a really tight third set that shouldn't happen. That's why I was freaking out inside and also outside today," said the two-time French Open finalist.

A nosebleed was one of Daniil Medvedev's biggest challenges in his win over Spanish qualifier Pedro Martinez, while Gael Monfils, who injured his racquet hand playing computer games before the tournament, downed Ivo Karlovic.

In the women's draw, Wimbledon champion Simona Halep stamped her class with a 6-2, 6-4 win over Britain's Harriet Dart, while Belinda Bencic knocked out former French Open champion Jelena Ostapenko, who was playing despite the sudden death of her father this month.

Two-time major winner Garbine Muguruza, who scaled Mount Kilimanjaro in the off-season as she searches for a return to form, dispatched home hope Ajla Tomljanovic 6-3, 3-6, 6-3.

Karolina Pliskova extended her winning streak, dispatching Germany's Laura Siegemund 6-3 6-3 to advance to the third round.

The Czech second seed is undefeated this year after winning six straight matches including the title at the Brisbane International earlier this month.

"For sure, the off-season I think was good. I did a lot of work, and I was feeling good in Brisbane," Pliskova, who made the semi-finals last year, told reporters.

"I like Australia. I always play well here. Of course it's only third round now, but I have played a lot of matches already, so I feel confident. I feel good enough to continue."

As Pliskova progressed, it was the end of the road for Carla Suarez Navarro, who in losing 6-3, 7-5 to Iga Swiatek has played her last match at the Australian Open. The 31-year-old Spaniard plans to retire from tennis at the end of the season.