Yoshihito Nishioka had never started a season better. The 21-year-old Japanese had reached the quarter-finals in Acapulco and the fourth round at the BNP Paribas Open in Indian Wells, the first time he had made the round of 16 at an ATP World Tour Masters 1000 tournament. In the desert, the left-hander had beaten then-No. 21 Ivo Karlovic and then-No. 14 Tomas Berdych for his biggest career win.

But in Miami, Nishioka had to retire from his second-round match against Jack Sock, and the news would get only worse: Nishioka had torn his ACL in his left knee and would require season-ending surgery.

“I had never injured my legs so I didn't know what was going on with my knee. I also didn't feel that much pain so I thought, 'No problem to keep playing'”, Nishioka told ATPWorldTour.com. “I don't know yet when I can come back on the ATP World Tour, but I'm already excited to be back and I want to be back soon is possible.”

The left-hander had already nearly eclipsed his win total from last season during the first three months of 2017. Nishioka had compiled a 9-9 match record this season, compared to his 10-12 record from all of 2016.

His successful start helped him reach his rankings goal for the year. Nishioka had wanted to crack the Top 60 of the Emirates ATP Rankings, which he did on 20 March at No. 58. “I always love to play in the U.S. and every time I play my best tennis there, so I knew could make good results at one or two of the tournaments, but I never thought I'd win so many matches at a high-level tournament,” Nishioka said of making the fourth round in Indian Wells.

The Japanese also won at least one round in six of the seven tournaments he played. In Acapulco, he qualified and went on to beat top American Jack Sock and Aussie Jordan Thompson before losing to eventual finalist Rafael Nadal.

“I felt from the beginning of the year that I had a chance to win against the top players so I kept trying and I took a chance in Acapulco against Sock,” Nishioka said. “Before I beat Sock, I thought the top players were much higher than me, so it would be very tough to win now with my level. But in Acapulco, I beat [Ryan] Harrison, Sock, Thompson, and I lost but played great tennis against Rafa. After Acapulco, I changed my mind to 'I can play with this level.' I think this is a very big reason that I made the round of 16 in Indian Wells.”

Nishioka underwent surgery earlier this month and has begun rehab in Japan.