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NEW YORK, Sept 5 (Reuters) - Australian youngster Alex de Minaur shrugged off a mid-match slump to stun 11th seed Karen Khachanov 6-4 0-6 4-6 6-3 6-1 in the U.S. Open third round on Saturday.
Khachanov started poorly, winning just 52% of his first-serve points and making 21 unforced errors en route to losing the opening set.
De Minaur, however, then suffered a mini-meltdown, losing eight games in a row, allowing Khachanov back into the match as the Russian opened up a 2-1 lead.
The 21-year-old Australian won only five points on his first serve in the second set and picked up a code violation late in the third for smashing his racket.
"It's not the way I want to conduct myself on the tennis court, it's not something that is normal for me, so I'm very disappointed in myself with the attitude I had," De Minaur said.
"I managed to kind of turn things around, but it's something that just can't happen and won't happen again."
With his stinging groundstrokes and impressive court coverage, De Minaur found a second wind to take a 3-0 lead in the fourth set before pulling away to force a fifth-set decider.
He finished with 42 winners and a staggering 29 points at the net to seal victory in just over three hours.
"I think probably the biggest thing that I did differently was kind of just shut up and play. That was kind of my mentality," he added.
De Minaur, the runner-up at last year's Next Gen ATP Finals, has reached the last-16 at Flushing Meadows for the second year in a row and will next meet Canadian Vasek Pospisil.