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 two hours on 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.
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* Big upset at Aussie Open
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, 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.
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 Williams is also one match closer to a historic 24th career major after making light work of Eugenie Bouchard to move into the Australian Open third round.
A seven-time winner at Melbourne Park, the 37-year-old blasted past the Canadian 6-2 6-2 in one hour and 10 minutes on Thursday night.
In a ruthless showing, Williams broke serve six times and cracked 20 winners - double that of Bouchard - but said it wasn't as easy as the score suggested.
"Genie has been to the finals of Wimbledon. She has been to the semi-finals of other grand slams so I said 'alright Serena, you have to come out hot and firing'," Williams said.
Williams will now meet Ukrainian Dayana Yastremska.
Other winners in the women's draw Thursday included reigning US Open champion Naomi Osaka, past US Open runners-up Karolina Pliskova and Madison Keys, No. 27-seeded Camila Giorgi and No. 28 Hsieh Su-Wei.
In the men's action, Novak Djokovic again got the better of Jo-Wilfried Tsonga at the Australian Open.
The No. 1-seed beat Tsonga 6-3, 7-5, 6-4 in the second round at Melbourne Park in a rematch of their 2008 final. This one started Thursday night and wrapped up after 12:30 a.m. on Friday.
"Certainly you could feel tension on the court from the beginning. I think we were both going through a lot of emotions," Djokovic said during an on-court interview.
Asked to elaborate on that sentiment at his news conference, Djokovic said: "Knowing the history ... I had with him, I guess that's what brought even more ... weight on this encounter tonight. I did feel a bit more nervy than I usually do."
Eleven years ago, Djokovic's victory over Tsonga gave the Serb the first of his 14 Grand Slam titles, a total that is tied with Pete Sampras for third most by a man, trailing only Roger Federer's 20 and Rafael Nadal's 17.
Djokovic is back at No. 1 in the ATP rankings and has won the past two major championships, at Wimbledon in July and the US Open in September, after dropping out of the top 20 last season following surgery to repair his right elbow.
Stan Wawrinka was up a set and was just two points away from taking the second against Milos Raonic, but couldn't do it.
Canadian Raonic held his nerve to win three successive tiebreaks and send the former Australian Open champion Wawrinka packing.
In a match lasting just over four hours that began under open skies and finished with the roof closed on Rod Laver Arena following a rain delay, Raonic triumphed 6-7 (4-7) 7-6 (8-6) 7-6 (13-11) 7-6 (7-5).
Switzerland's Wawrinka, who won the Open title back in 2014, was up a break late in the fourth set but it was the big-serving Raonic who finished the stronger.
"That is hard to describe - it feels like four hours passed by in 15 minutes," said Raonic.
"In the heat of the battle, the adrenaline takes over. You try to do everything you can each and every point.
"I was very fortunate to stay alive in that fourth set. I am thankful that it was indoors. I do a little bit better indoors than I do outdoors ... thank you for raining."
Raonic's third-round opponent will be Frenchman Pierre-Hugues Herbert, who equalled his best grand slam result by upsetting last year's surprise semi- finalist Hyeon Chung.
Herbert triumphed 6-2 1-6 6-2 6-4 against the No 24 seed from South Korea.
No 8 seed Kei Nishikori continued his unbeaten start to 2018, edging towering Croatian Ivo Karlovic on Thursday in a super-tiebreak.
Karlovic served 59 aces in the match - but crucially just one in the deciding tiebreaker - as Nishikori prevailed 6-3 7-6 (8-6) 5-7 5-7 7-6 (10-7).
Nishikori broke Karlovic's serve just once in the marathon encounter lasting three hours and 48 minutes, but that proved too be enough.
"It was a really tough match and it could have gone both ways," said Nishikori, who has reached the last eight at Melbourne Park on three previous occasions.
"I was down 7-6 in the tiebreak but I focused well in the last points and I'm really happy to win."
The Japanese star did well to keep his cool when Karlovic made a successful challenge at a crucial moment in the super-tiebreak after his return was wrongly called out despite clipping the baseline.
The chair umpire then awarded the point to the Croatian after determining the linesperson's erroneous call did not affect Nishikori's subsequent shot which he dumped into the net, levelling the score at 6-6.
Nishikori will play German Philipp Kohlschreiber or Portugal's Joao Sousa in the third round on Saturday.
Italian No 12 seed Fabio Fognini also benefited by saving his best for the tiebreaks, downing Argentina's Leonardo Mayer 7-6 (7-3) 6-3 7-6 (7-5) to set up a third-round battle with Pablo Carreno Busta from Spain.
The 23rd-seeded Carreno Busta beat Ilya Ivashka from Belarus 6-2 6-3 7-6 (9-7).