"My opponent is a great grass court player so I had difficulty reacting to his serves but it was good I managed to win in four sets. I'm glad I'm back and healthy," he said, adding that his lingering hip injury was not a concern.
Nishikori, who is Japan's most successful tennis player with 11 ATP Tour titles, next faces a tricky test to overcome Spanish 18th seed Roberto Bautista Agut and advance to the fourth round for a third time since his Wimbledon debut in 2008.
Rising teenager Osaka put in an impressive performance to beat Czech 22nd seed Barbora Strycova 6-1 0-6 6-4 and will face five-time champion Venus Williams in the third round.
The duo were scheduled to meet in January's Auckland Open but Venus withdrew through injury, and Osaka is delighted she finally has a chance to face one of her idols.
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"I can't believe I'll be facing Venus Williams, someone I've been watching on TV. If it weren't for (the Williams sisters) I wouldn't be playing tennis. I feel like all my life I've been preparing for this one match. I'll do my best," she said.
The in-form Yuichi Sugita can become the third Japanese player to reach the third round, after managing a first ever Wimbledon win on Tuesday, if he beats France's Adrian Mannarino on Thursday.
(Reporting by Aditi Prakash in Bengaluru; Editing by John O'Brien)
