World number one Novak Djokovic's quest for a calendar Grand Slam and record-breaking 21st major title remains on track after outlasting Jenson Brooksby 1-6 6-3 6-2 6-2 in a gruelling US Open showdown.
Unheralded American qualifier and world number 99 Brooksby had the crowd roaring following an incredible opening set against Djokovic in Monday's last-16 clash at Flushing Meadows.
However, Djokovic – bidding to become only the third man to sweep all four slams in the same year and first since Rod Laver in 1969 – responded to the almighty challenge, showcasing his superior physicality as the three-time US Open champion rallied into the quarter-finals in New York.
Brooksby was making his first appearance on Arthur Ashe Stadium, where the 20-year-old was looking to become the lowest-ranked player to beat a number one at the US Open since the start of the ATP rankings in 1973 and youngest American man since Andy Roddick (2003 Wimbledon) to reach a major quarter-final.
He was not overawed on the big stage, blitzing Djokovic in a remarkable first set. Playing with a bounce in his step and bringing the crowd to its feet, Brooksby only hit one unforced error in a dominant 29-minute display, which included two breaks of serve.
Djokovic was 38-34 at grand slams when losing the opening set and 12-10 at Flushing Meadows and after an error-filled opener, the Serb star let out an almighty roar after racing out to a 3-0 lead.
Just as Djokovic – level on 20 men's slams with Rafael Nadal and Roger Federer – looked comfortable, he endured a marathon 20-minute fifth game against Brooksby.
Brooksby broke at the sixth time of asking and the breath-taking tennis continued as Djokovic broke straight back to reclaim his advantage at 4-2 – the latter ending the game with an intense stare down in the direction of his opponent.
After a gruelling second set to level the match, the third followed a similar pattern, with Djokovic breaking in the opening game before moving 3-0 ahead.
Djokovic did not relinquish that lead, hitting 13 winners while claiming 11 of his 13 points at the net as he took the match to Brooksby.
Brooksby put up a huge fight but, he was unable to maintain his charge as the crowd went silent – Djokovic looking ahead to a last-eight showdown with sixth seed Matteo Berrettini in a rematch of the Wimbledon final.
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With his hard-fought victory, which lasted almost three hours, Djokovic improved to 11-0 against Americans at the US Open. He is 29-3 at major events and 70-10 in ATP Tour-level matches. The 34-year-old is on a 21-match winning streak against players from the United States since Sam Querrey snapped his 30-match slam streak at Wimbledon in 2016.
WINNERS/UNFORCED ERRORS
Djokovic – 44/41
Brooksby – 27/28
ACES/DOUBLE FAULTS
Djokovic – 9/1
Brooksby – 4/1
BREAK POINTS WON
Djokovic – 6/12
Brooksby – 3/11