Alcaraz begins Japan Open defence with win over Michelsen

The Spanish world number three struggled to find his rhythm early on, spraying shots long or into the net as the big-serving American stayed aggressive.

He pulled away in the tie-break but was pinned back in the second set, with Michelsen, ranked 34th, gaining parity after a marathon 10th game.

From there, though, the seven-time Grand Slam champion suddenly found form, mixing a barrage of blistering aces with delicate volleys to nullify his opponent's threat.

It was ultimately a heartening performance for Alcaraz, who only returned to action at the US Open in August after a four-month injury layoff.

He will play Italy's Matteo Arnaldi, ranked 37th, in the next round.

Earlier, second-seeded Frances Tiafoe cruised past Kei Nishikori 6-4, 6-4 in the beloved home star's final career match.

Nishikori, Asia's most decorated men's tennis player, said in May he was calling time on a career that might have taken him to the pinnacle of the game were it not for persistent injury.

"I am happy that in my spirit I remained competitive until the end," he said in an emotional post-match ceremony.

In other matches, Spanish qualifier Jaume Munar upset third-seeded Taylor Fritz, the 2022 champion, 7-6 (9/7), 4-6, 6-3.

Sixth seed Casper Ruud also crashed out to Luciano Darderi of Italy, 7-6 (7/3), 6-3.

And fifth-seeded American Brandon Nakashima also left the tournament with a 6-3, 6-2 defeat to Frenchman Ugo Humbert.