Novak Djokovic struggled but advanced within three matches of completing the first men's singles calendar-year Grand Slam in 52 years on Monday by outlasting American Jenson Brooksby at the US Open.
World number one Djokovic rallied past 99th-ranked Brooksby 1-6, 6-3, 6-2, 6-2 to book a quarter-final encounter with Italian sixth seed Matteo Berrettini in a rematch of July's Wimbledon final.
The 34-year-old Serbian star would become the first man since Rod Laver in 1969 to sweep all four major titles in the same year by capturing his fourth career US Open crown.
Djokovic also seeks a men's singles record 21st Slam trophy, which would boost him one ahead of "Big Three" rivals Roger Federer and Rafael Nadal, both absent with injuries. In all, Djokovic won 15 of the last 20 games, rolling to victory in the stamina test after two hours and 59 minutes.
Tokyo Olympic champions Alexander Zverev and Belinda Bencic advanced with straight-set triumphs, as did British 18-year-old qualifier Emma Raducanu.
German fourth seed Zverev stretched his win streak to 15 matches by beating Italian 13th seed Jannik Sinner 6-4, 6-4, 7-6 (9/7). Swiss 11th seed Bencic eliminated Polish seventh seed Iga Swiatek, last year's French Open champion, 7-6 (14/12), 6-3.
And 150th-ranked Raducanu ripped 43rd-ranked American Shelby Rogers 6-2, 6-1 in 66 minutes.