NEW YORK (Reuters) - Fifth seed Alexander Zverev fought off a spirited challenge from American wildcard Brandon Nakashima to claim a 7-5 6-7(8) 6-3 6-1 victory in the second round of the U.S. Open on Wednesday.
Zverev did not drop his serve but was stretched to four sets by teenager Nakashima, ranked 223 in the world.
While the German sent down 24 aces and looked ominous on first serve, he struggled on his second delivery, dropping to as low as 11% of second-serve points won in the second set.
"I didn't get broken even though my second serve was shaky a little bit," the 23-year-old said. "My backhand was shaky too. I will have to go practise some more."
Zverev was on the front foot from the start against Nakashima but failed to convert three break point opportunities in the fifth game.
Nakashima, who defeated Italian Paolo Lorenzi on his Grand Slam main draw debut on Monday, led 40-0 on serve in the 11th game but went off the boil as Zverev took a 6-5 lead.
Zverev clinched the opening set before Nakashima, who reached the U.S. Open junior semi-finals last year, came out fighting with relentless baseline hitting.
Nakashima, coached by 1987 Wimbledon champion Pat Cash, earned two set points in the second with a delicate drop shot but another lapse in concentration allowed Zverev to force a tiebreak.
Despite taking a 5-0 lead, Nakashima needed a further five set points and a Zverev double fault to level the contest.
Zverev made an early break in the third set before unleashing his booming forehands to break Nakashima's serve three times in the fourth en route to victory on a humid afternoon at Flushing Meadows.
Zverev will next face Frenchman Adrian Mannarino, who defeated home favourite Jack Sock 7-6(5) 7-5 6-2.
(Reporting by Hardik Vyas in Bengaluru,; Editing by Toby Davis and Ed Osmond)