MELBOURNE, Australia -- For several years now, Alexander "Sascha" Zverev has been touted as the dazzling future of tennis.

On Saturday at the Australian Open, the gangly 19-year-old from Hamburg, Germany, demonstrated that he is on the very cusp of that predicted greatness.

But he's not quite there yet.

In a bruising, epic match, 14-time Grand Slam winner Rafael Nadal ultimately prevailed in the third round, 4-6, 6-3, 6-7 (5), 6-3, 6-2.

The match required 4 hours, 6 minutes. Midway through the final set, leg cramps appeared to afflict Zverev, who called for the ATP World Tour trainer.

How did Nadal beat Zverev?

"Fighting," Rafa said in his on-court interview. "And running a lot.

"Everybody knows how good Alexander is. He's the future of our sport, and the present also."

Zverev, who stroked 74 unforced errors, failed in his attempt to advance to the second week of a major for the first time. But it's only a matter of time, perhaps as soon as the French Open later this year.

This was a classic battle between a 30-year-old champion and a gifted teenager with similar aspirations of greatness. The two had a singular history going back to last year's event at Indian Wells, California, where Zverev had a match point against Nadal, but eventually lost a grinding three-set match.

This match underlined just how close Zverev is -- and how far the 6-foot-6, 189-pound player has to go to beat a legend in the crucible of a Grand Slam.

Down the stretch, Zverev's verve and nerve left him, resulting in a double fault, a loose forehand or two and a general lack of focus. When his legs started to go, it was all over.

Thus, Nadal will play Gael Monfils in Monday's fourth round. The Frenchman defeated Philipp Kohlschreiber 6-3, 7-6 (1), 6-4 in Saturday's late clash on Hisense.

Nadal is in comeback mode yet again. A wrist injury forced him to withdraw from last year's French Open after a second-round win and he missed Wimbledon.

Clearly, he is not the player he once was. The No. 9 seed lost the crucial third-set tiebreaker when he was overpowered by a massive Zverev backhand winner and struggled at times on his service games.

But here's the good news for Nadal: After going six consecutive Grand Slam matches with a defeat in which he dropped the first set, he scored an impressive comeback. For someone who needs match wins to build confidence, this was an important match.

Losing the third-set tiebreaker, Nadal said, provided him with the critical mass to turn the match around.

"After that, I said, 'I need to fight for every point -- forget about the result,'" Nadal said.

"I see that he suffered a lot. Sometimes you get cramps because you are tired a little bit, and sometimes because of nerves."

No one has ever accused Nadal of lacking nerve. At a precarious time in his career, all those exuberant scissor kicks and upper cuts he displayed against Zverev should sustain him going forward.

Spain's David Ferrer lost to countryman Roberto Bautista Agut. GREG WOOD/AFP/Getty Images

In later action, Grigor Dimitrov and Richard Gasquet may have had the latest start to a match at the Australian Open -- organizers couldn't confirm -- but fell well short of the record for the latest finish.

The third-round match started at 11:58 p.m. local time. After grinding through four games in 24 minutes, No. 15-seeded Dimitrov picked up pace and finished off 6-3, 6-2, 6-4 at 2 a.m. -- well short of the latest-finishing match in Grand Slam history.

In 2008, Lleyton Hewitt and Marcos Baghdatis started a match here at 11:47 p.m. and ended at 4:34 a.m. For the record, Hewitt won 4-6, 7-5, 7-5, 6-7 (4), 6-3.

In other action, No. 13 seed Roberto Bautista Agut came out on top in the all-Spanish clash with David Ferrer, as he advanced to Round 4 with a 7-5, 6-7 (6), 7-6 (3), 6-4 victory. He will face third seed Milos Raonic next after the Canadian, who reached the semifinals in Melbourne last year, defeated Gilles Simon 6-2, 7-6 (5), 3-6, 6-3 on Hisense.

Denis Istomin followed his upset win over defending champion Novak Djokovic with a 6-4, 4-6, 6-4, 4-6, 6-2 win over Pablo Carreno Busta, reaching the fourth round.

On Thursday, Istoman, a wild-card entry from Uzbekistan, became the lowest-ranked player -- at 117 -- to beat a second-seeded player at the Australian Open.

Istomin beat Djokovic on the main Rod Laver Arena, but his match Saturday was on the much lower-profile Show Court 2. He will next play DImitrov.

No. 8 Dominic Thiem beat Benoit Paire 6-1, 4-6, 6-4, 6-4 to set up a fourth-round match against No. 11 David Goffin, who ended Ivo Karlovic's run 6-3, 6-2, 6-4.

Karlovic's win in the first round set an endurance record -- the 84 games in the win over Horacio Zeballos, which ended 22-20 in the fifth, was an Open-era mark for the tournament.

The Associated Press contributed to this report.