Sixth-seeded Matteo Berrettini of Italy was made to work hard at the US Open as he battled past qualifier Oscar Otte of Germany 6-4, 3-6, 6-3, 6-2 to reach the quarterfinals at Flushing Meadows for a second time.

The 25-year-old Italian, who reached his first major final at Wimbledon before losing to world No 1 Novak Djokovic, was tested by Otte, surviving a dip in the second set, before raising his intensity to advance after two hours and 22 minutes. The German struggled with a wrist injury throughout the fourth set after falling at 1-1 in the set, but continued to toil. "It was an intriguing match, as I expected. Different court, tricky player. I wasn`t feeling really good at the beginning," Berrettini said. "I had to adjust to the conditions and it was a match that I knew I could win and it`s never easy when it`s like that.