“It was very hard for me, to beat two Top 10 guys. And (Grigor) Dimitrov also was playing well. It was one of the greatest weeks for me. It’s unfortunate to get injured but it’s still a very exciting week.”—Kei Nishikori, in a press conference announcing his withdrawal from the Miami Masters 1000 with a left groin injury before his semfinal meeting with world No. 2 Novak Djokovic.

MIAMI, Fla.—Kei Nishikori is just 24 years old and he’s already had his share of injuries. He’s retired 11 times in his career (twice this year) and withdrawn three times, counting today's sudden announcement. Nishikori has proven somewhat fragile, which is problematic in a number of ways—not least because he plays such a high-effort, physically draining style of tennis.

Nishikori has been struggling with this groin pull for weeks; he retired in mid-February during his second-round match with Teymuraz Gabashvili at Delray Beach. The injury trailed him to Indian Wells, where he lost a third-round match to Tommy Haas. Nishikori played through the pain for more than a week here, but the strain of his workload only aggravated his condition. Still, he ended up having what might be the best tournament of his career.

Nishikori’s run began with a routine win over Marinko Matosevic and picked up pace with a victory over the emerging star Dimitrov. In the fourth round, Nishikori met No. 4 seed David Ferrer and survived four match points enroute to a 7-6 in-the-third win. He backed that one up with a terrific effort against Roger Federer, coming back from the loss of the first set to win in three. He said of that win:

“To win against Roger was a big achievement for me. Still, those top two guys (Djokovic and Rafael Nadal) are different, stronger. I think I have enough power to play with them and I’m always believing in myself. I thought this was going to be a great challenge for me.”

While some critics may grumble at Nishikori having pulled out when he practiced yesterday—and not making his decision until after today’s pre-match warm-up—his choice was in some ways a boon to fans. Ticket holders for today’s day session will be able to exchange their reservations for a day next year because the evening session featuring Rafael Nadal is a sell-out and few tickets remain for the weekend. The only other match on the day card today was a women’s doubles semifinal, won by Martina Hingis and Sabine Lisicki.

This is the second time in three years that the day session featuring just one singles match has been ruined by a withdrawal. In 2012, Nadal gave Andy Murray a walkover at the same stage.

“It’s really sad,” said Nishikori, who will wait until he’s examined by doctors before he decides about taking part in Japan’s upcoming Davis Cup quarterfinal tie at home against the Czech Republic. “It’s the semifinals of one of the biggest tournaments and I was playing well.”

Still, Nishikori has a lot more to build on now. He’s won four titles and reached the semis of a Masters 1000 before (Shanghai, in 2011), but in many ways this tournament should be considered a breakthrough.