MELBOURNE, Australia (AP) -- Push Simona Halep to the brink, and she summons her best.
The Australian Open's top-seeded woman got all she could handle from 20-year-old American Sofia Kenin in the second round before taking the last four games to emerge with a 6-3, 6-7 (5), 6-4 victory that took 2 1/2 hours Thursday.
"Well, I have no idea how I won this tonight," said Halep, the reigning French Open champion. "It's so tough to explain what happened on court."
A year ago at Melbourne Park, Halep was a point from being eliminated in two matches but came back each time en route to reaching the final. In the first round this year, she was down a set and a break before turning things around. And this time, against a hard-hitting Kenin, Halep trailed 4-2 in the third set and managed to not cede another game.
And that was despite getting what she described as "a little bit injured" in the second set, something that seemed clear from the way she wasn't always able to run with her usual verve.
"Hopefully," said Halep, whose No. 1 ranking is up for grabs during the Australian Open, "next round I play better."
That third-round matchup will be quite intriguing, because it'll be against seven-time Grand Slam champion and former No. 1 Venus Williams. And the winner of that could face Williams' younger sister, 23-time major champ Serena, in the fourth round.
Venus won a three-setter that finished a little before Halep's did -- and in much more emphatic fashion. Pushed to that deciding set by getting broken to end the second, Venus ran away with the win down the stretch, defeating Alize Cornet 6-3, 4-6, 6-0.
So what was the difference in the lopsided third set?
"She was just putting more intensity than me. She was hitting harder, deeper," Cornet said. "I had a little less energy than in the second set and she took advantage of it and really raised her level."
The 38-year-old Venus, unseeded at a major for the first time in five years, was the runner-up in Australia to Serena in 2003 and 2017.
Serena advanced to the third round by beating 2014 Wimbledon finalist Eugenie Bouchard 6-2, 6-2, reeling off the last five games and 16 of the final 20 points. That match was followed in Rod Laver Arena by No. 1 Novak Djokovic's 6-3, 7-5, 6-4 victory over Jo-Wilfried Tsonga in a rematch of the 2008 final at Melbourne Park.
That one ended in the wee hours of Friday, just after two-time major champion Garbine Muguruza and Johanna Konta got going at 12:30 a.m. in what is believed to be the latest-starting match in tournament history. Muguruza eventually won 6-4, 6-7 (3), 7-5 at 3:12 a.m.
Other winners in the women's draw included reigning U.S. Open champion Naomi Osaka, past U.S. Open runners-up Karolina Pliskova and Madison Keys, No. 27-seeded Camila Giorgi and No. 28 Hsieh Su-Wei.
In men's action, Stan Wawrinka was up a set and was just two points away from taking the second against Milos Raonic. Couldn't do it.
About an hour later, 2014 champion Wawrinka was a single point from grabbing the third set. Denied again.
And another hour after that, Wawrinka was two points from seizing the fourth to force a fifth. Nope, not on this afternoon.
Wawrinka kept coming oh-so-close, and Raonic kept hanging in there and toughing out the most important moments along the way to a 6-7 (4), 7-6 (6), 7-6 (11), 7-6 (5) victory that put the 16th-seeded Canadian into the third round.
"I missed a few little points," Wawrinka said, "that could have changed the match."
"It feels like 4 hours passed by in about 15 minutes. ... The adrenaline takes over," said Raonic, the runner-up at Wimbledon in 2016. "I was very fortunate to stay alive in that fourth set."
They were interrupted for about a half-hour while the roof at Rod Laver Arena was shut because of rain at 4-all in the third set.
Raonic thought that helped him quite a bit.
"I do a little bit better indoors than outdoors," he said, "so thank you for raining up there."
In other men's action on Day 4, No. 4 seed Alexander Zverev won in five sets and 2014 U.S. Open runner-up Kei Nishikori withstood 59 aces from 39-year-old Ivo Karlovic en route to a 6-3, 7-6 (6), 5-7, 5-7, 7-6 (7) victory, but No. 7 Dominic Thiem retired from his match in the third set after dropping the first two, and 2018 Australian Open semifinalist Hyeon Chung lost to Pierre-Hugues Herbert 6-2, 1-6, 6-2, 6-4.
Raonic delivered 39 aces, part of an impressive ratio of 84 total winners to only 44 unforced errors.
This was a matchup probably better suited to the second week than the second round of a Grand Slam tournament, given both men's credentials. But Wawrinka, a three-time major champion once ranked as high as No. 3, dropped out of the top 250 last season, when he had surgery on his left knee.
His signature one-handed backhand is as dangerous as ever -- he had a 16-2 edge in winners on that shot Thursday -- and he hit 28 aces of his own. But as even as the match was in many respects -- Raonic only won two more points overall, 163-161 -- Wawrinka couldn't come through when he really needed to.
Raonic had plenty to do with that, of course, including in the third-set tiebreaker, when he served his way out of trouble.
Wawrinka's three set points there came at 6-5, when Raonic delivered a serve at 129 mph (208 kph) followed by a forehand volley winner; at 8-7, when Raonic's 125 mph (201 kph) serve drew a missed return; and at 10-9, when an ace at 132 mph (213 kph) did the trick. A 123 mph (198 kph) service winner gave Raonic that set.
In the last tiebreaker, Wawrinka was up 5-4 before Raonic closed with three consecutive points to avoid heading to a fifth set.
"Today, I'm sad and frustrated," Wawrinka said. "But in general, if I take some distance with it, I'm happy to see that I'm able to play again with this level, able to move that well."