World No. 4 Kei Nishikori was made to work hard by 57th-ranked Federico Delbonis of Argentina to advance to the Miami Open men's singles quarterfinals with a 6-3, 4-6, 6-3 victory on Tuesday.
After taking the first set with ease, Nishikori started making sloppy mistakes in the second as a troublesome left knee started hindering his movement. After receiving treatment, the Japanese dropped three straight games to see the match at Crandon Park Tennis Center leveled at 1-1.
Despite needing three fourth-round sets to get there, the 27-year-old qualified for the quarterfinals for the fourth straight year and will be looking to improve on his semifinal finish last year. His 2016 effort was his best performance in seven appearances at the Florida tournament.
"After I dropped the second set, I told myself I have to focus again. I got a little better in the third but was helped by my opponent's mistakes, too," said Nishikori.
"The matches will get tougher from the next round so I hope to push myself and keep my spirits up," he said.
Nishikori said after the match that the injury is not serious as his knee just tends to ache when he becomes extremely fatigued, and he just needed the break to receive a massage.
In the quarterfinals on Wednesday, Nishikori will face 40th-ranked Fabio Fognini of Italy, whom he has a 2-0 head-to-head record against. Fognini defeated American Donald Young 6-0, 6-4 to advance.
Top seed and world No. 3 Stan Wawrinka suffered a surprise 4-6, 6-2, 6-1 collapse to Alexander Zverev of Germany. Fourth and fifth seeds Roger Federer and Rafael Nadal advanced safely.
Should Nishikori beat Fognini, he will face the winner of the Nadal-Jack Sock match in the semifinals.