Serena Williams won a tremendous battle against world number one Simona Halep to reach the quarter-finals of the Australian Open but believes she will need to find a new level if she is to win a 24th grand slam singles title.
Halep was in the unusual position of going into the match as the number one seed but also the underdog against a player she had beaten just once in nine previous encounters.
The Romanian, who saw off Venus Williams in the previous round, dug in superbly after losing a one-sided opening set to force a decider, and might well have come out on top had she broken for 4-2.
But Williams saved three break points, broke Halep in the following game and served out a 6-1 4-6 6-4 victory to set up a last-eight meeting with Karolina Pliskova.
Williams said of Halep's comeback: "That's why she's number one. She literally lifted her game to a new level. I didn't.
"But it's a part of this journey on my way back. It's 10 months, so I can't be too upset at myself. I felt like I did have an opportunity to win that in straight sets, but then I'm playing the number one player in the world.
"So I'm still learning, which is, at my age and my point in my career, I think admirable and exciting.
"I think today I'm just learning that I can, I have to, fight for titles. I have to fight for matches. Actually, I don't have any titles yet, but just fighting for matches is really important.
"I think overall I'm hanging in there. I'm solid. I can definitely go to a new level. I have to if I want to stay in the tournament."
Halep arrived in Melbourne on a five-match losing streak and admitting she felt under-prepared so, although she lost this match and might well lose her number one ranking as well, she was not downhearted.
The French Open champion said: "I will start with a joke. I felt like I had been hit by a train in the first set. Everything was too fast.
"I didn't get scared about the first set, because I knew I have a better level, and I can play better if I stay there and I really start moving better and hitting the ball stronger.
"So after the first set, I got fire inside myself, and I said that now I start the match."
Halep said she had no regrets about the missed break points, adding: "She served really well those points. I tried to be aggressive that game. I have been aggressive. I was unlucky a little bit, let's say, in that moment."
Halep, meanwhile, insisted she has not yet hired Thierry van Cleemput as her new coach despite the Belgian joining her for her warm-up only two days after splitting from David Goffin.
"We are talking," she said. "I have nothing to do with their split."
Williams now takes on seventh seed Pliskova, who has been under the radar so far but produced a masterful display to beat Garbine Muguruza 6-3 6-1, hitting 23 winners and only three unforced errors.
The Czech beat Williams in the US Open semi-finals in 2016 but lost in the quarter-finals last summer.
"I didn't play well that match, so for sure it would be good revenge to play her again," said Pliskova. "Different conditions here, I think I'm playing a little bit better than I was last year, so I'm looking forward to it."
US Open champion Naomi Osaka recovered from a set down for the second consecutive match, defeating Anastasija Sevastova 4-6 6-3 6-4 to reach her first Australian Open quarter-final.
The Japanese player, who is half Haitian, then revealed how her visits to the country of her father's birth have inspired her.
She said: "It's a very humbling experience to go back, because you see so many people that they don't have much, and then you go back to your house and everything that you take for granted you start appreciating it more."
In the last eight, Osaka will play sixth seed Elina Svitolina, who saved five break points in the third game of the deciding set on her way to a 6-2 1-6 6-1 victory over Madison Keys.