Melbourne: If Rafael Nadal wanted a fitness test in the first week, he got one in his almost four-hour, 6-3, 6-7 (4), 6-3, 6-3 win over Diego Schwartzman.
After embracing at the net, his spot in a 10th Australian Open quarterfinal secure, top-ranked Nadal draped an arm around his Argentine friend and patted him on top of the head.
"A great battle ... he's a good friend of mine," Nadal said. "This is the first big match that I played in 2018. One match like this probably helps. That's confidence for myself, that's confidence I can resist for four hours on court at a good intensity."
Nadal lost last year's Australian Open final in five sets to Roger Federer, but went on to regain the No. 1 ranking and win the French and U.S. Open titles before bringing his season to a premature end because of an injured right knee.
He didn't play a competitive match before the season-opening major, and advanced through three rounds without dropping a set.
That streak finished when Schwartzman took the second set to level the match, rebounding three times after dropping serve to break back against Nadal.
The key game of the fourth set lasted almost 13 minutes and 20 points, with Nadal finally holding after saving five break points as Schwartzman attacked him with everything he had.
The 16-time major winner broke again in the next game and withstood more break points - seven in all in the last set and 15 of 18 in the match - before clinching it in 3 hours, 51 minutes.
Nadal will next play sixth-seeded Marin Cilic, who collected his 100th Grand Slam match win with a 6-7 (2), 6-3, 7-6 (0), 7-6 (3) victory over No. 10 Pablo Carreno Busta.
"It was a big battle. I was really relieved I played such a good tiebreaker at the end," the 2014 U.S. open winner said. Of his Grand Slam milestone, Cilic said he hadn't been aware of it before the match "but it's beautiful to hear.
"I had the 300th win of my career at the U.S. Open in 2014, so this is also beautiful one. I hope I'm going to continue and gather three more here."
Kyle Edmund reached his first Grand Slam quarterfinal and continued 33-year-old Andreas Seppi's long drought with a 6-7 (4), 7-5, 6-2, 6-3 win on Hisense Arena.
Seppi has now played 52 majors without reaching the quarterfinals - he has lost in the fourth round five times.
Caroline Wozniacki continued to cash in on her second chance, reaching the quarterfinals here for the first time since 2012 with a 6-3, 6-0 win over Magdalena Rybarikova.
After saving two match points and coming back from 5-1 down in the third set of her second-round win, No. 2-ranked Wozniacki said she was "playing with the house money" and had nothing to lose.
"I think being almost out of the tournament, you have nothing to lose after that," Wozniacki said. "I played really well from being down 5-1 ... since then I've just kept that going."
She has won both matches since in straight sets and will next play Carla Suarez Navarro, who came back from a set and 4-1 down to beat No. 32 Anett Kontaveit 4-6, 6-4, 8-6.
After a tight tussle in the opening four games against No. 19-seeded Rybarikova, a Wimbledon semifinalist last year, Wozniacki dominated the fourth-round match and conceded only six points in the second set. She even tried a between-the-legs "tweener" from near the baseline for the first time in a tour-level match. She didn't win the point, but said it was progress.
"I think you can tell my confidence is high," Wozniacki, who finished last season by winning the WTA Finals title, said in an on-court TV interview. "I tried a tweener today and it went in."
She looked at a replay on the stadium screen and joked "I'm admiring myself there."
Elise Mertens reached the quarterfinals in her debut in the Australian Open main draw, beating Petra Martic 7-6 (5), 7-5 to extend her winning streak to nine matches including her run to the Hobart International title last week.
"It's been amazing - good start of the year," Mertens said. "This is really a bonus."