<p>Novak Djokovic was sensationally disqualified from the US Open on Sunday after striking a lines official with a ball during his last-16 match.</p>.<p>The world number one went 5-6 down in the first set to Spain's Pablo Carreno Busta when he hit a ball in the direction of the female official.</p>.<p>It struck her in the throat and she could be heard gasping.</p>.<p>Djokovic rushed over to check that she was okay and after a few minutes she got up and walked off the court.</p>.<p>Following around ten minutes of discussions with the tournament referee, the umpire declared that Carreno Busta had won by default.</p>.<p>Djokovic shook hands with Carreno Busta before leaving the court.</p>.<p>The Serbian star is only the third player in Grand Slam history to be disqualified out of a men's singles tournament following John McEnroe at the Australian Open in 1990 and Stefan Koubek at the French Open in 2000.</p>.<p>Djokovic had been chasing an 18th Grand Slam title at the Billie Jean King US National Tennis Center.</p>.<p>He was hoping to close the gap on Roger Federer and Rafael Nadal, both absent from the tournament, in the race for the all-time men's Slam singles title record.</p>.<p>Djokovic is on 17, with Nadal on 19 and Federer on 20.</p>.<p>Earlier, American Jennifer Brady led a day of upsets in the women's draw.</p>.<p>Brady, the 28th seed, stunned three-time Grand Slam winner Angelique Kerber of Germany to reach a Grand Slam quarter-final for the first time in her career.</p>.<p>The 25-year-old took just 1hr 29min to sweep aside the 17th seed 6-1, 6-4 to move into the last eight at Flushing Meadows.</p>.<p>"It's awesome. Hopefully I keep going," she told reporters.</p>.<p>Brady, whose previous best appearances at Slams were fourth-round finishes at the Australian and US Opens three years ago, credited her run to becoming fitter.</p>.<p>Brady will play Yulia Putintseva for a spot in the last four after the Kazakhstan 23rd seed stunned eighth seed Petra Martic of Croatia elsewhere on Sunday.</p>.<p>Putintseva displayed a range of exquisitely placed dropshots as she sent Martic tumbling out 6-3, 2-6, 6-4 in 2hr 37 min inside Arthur Ashe Stadium.</p>.<p>Later, two-time Grand Slam winner Naomi Osaka looks to move into the last eight at the expense of Estonian 14th seed Anett Kontaveit.</p>.<p>Sixth seed Petra Kvitova is also in action against unseeded American Shelby Rogers.</p>.<p>In the men's draw Sunday, fifth seed Alexander Zverev became the first German to reach the US Open last eight since Tommy Haas in 2007.</p>.<p>Zverev, the fifth seed, bulldozed Spain's unseeded Alejandro Davidovich Fokina 6-2, 6-2, 6-1 in just 1hr 34 min.</p>.<p>Later in the men's draw, seventh-seeded David Goffin from Belgium goes up against Canadian 12th seed Denis Shapovalov.</p>
<p>Novak Djokovic was sensationally disqualified from the US Open on Sunday after striking a lines official with a ball during his last-16 match.</p>.<p>The world number one went 5-6 down in the first set to Spain's Pablo Carreno Busta when he hit a ball in the direction of the female official.</p>.<p>It struck her in the throat and she could be heard gasping.</p>.<p>Djokovic rushed over to check that she was okay and after a few minutes she got up and walked off the court.</p>.<p>Following around ten minutes of discussions with the tournament referee, the umpire declared that Carreno Busta had won by default.</p>.<p>Djokovic shook hands with Carreno Busta before leaving the court.</p>.<p>The Serbian star is only the third player in Grand Slam history to be disqualified out of a men's singles tournament following John McEnroe at the Australian Open in 1990 and Stefan Koubek at the French Open in 2000.</p>.<p>Djokovic had been chasing an 18th Grand Slam title at the Billie Jean King US National Tennis Center.</p>.<p>He was hoping to close the gap on Roger Federer and Rafael Nadal, both absent from the tournament, in the race for the all-time men's Slam singles title record.</p>.<p>Djokovic is on 17, with Nadal on 19 and Federer on 20.</p>.<p>Earlier, American Jennifer Brady led a day of upsets in the women's draw.</p>.<p>Brady, the 28th seed, stunned three-time Grand Slam winner Angelique Kerber of Germany to reach a Grand Slam quarter-final for the first time in her career.</p>.<p>The 25-year-old took just 1hr 29min to sweep aside the 17th seed 6-1, 6-4 to move into the last eight at Flushing Meadows.</p>.<p>"It's awesome. Hopefully I keep going," she told reporters.</p>.<p>Brady, whose previous best appearances at Slams were fourth-round finishes at the Australian and US Opens three years ago, credited her run to becoming fitter.</p>.<p>Brady will play Yulia Putintseva for a spot in the last four after the Kazakhstan 23rd seed stunned eighth seed Petra Martic of Croatia elsewhere on Sunday.</p>.<p>Putintseva displayed a range of exquisitely placed dropshots as she sent Martic tumbling out 6-3, 2-6, 6-4 in 2hr 37 min inside Arthur Ashe Stadium.</p>.<p>Later, two-time Grand Slam winner Naomi Osaka looks to move into the last eight at the expense of Estonian 14th seed Anett Kontaveit.</p>.<p>Sixth seed Petra Kvitova is also in action against unseeded American Shelby Rogers.</p>.<p>In the men's draw Sunday, fifth seed Alexander Zverev became the first German to reach the US Open last eight since Tommy Haas in 2007.</p>.<p>Zverev, the fifth seed, bulldozed Spain's unseeded Alejandro Davidovich Fokina 6-2, 6-2, 6-1 in just 1hr 34 min.</p>.<p>Later in the men's draw, seventh-seeded David Goffin from Belgium goes up against Canadian 12th seed Denis Shapovalov.</p>