Kei Nishikori saves four match points to knock out David Ferrer at Sony Open

Kei Nishikori was sharp and resilient in his upset of David Ferrer on Tuesday afternoon. (Clive Brunskill/Getty Images) Kei Nishikori followed up his good

Kei Nishikori was sharp and resilient in his upset of David Ferrer on Tuesday afternoon. (Clive Brunskill/Getty Images)

Kei Nishikori followed up his good victory over No. 16 Grigor Dimitrov in the third round of the Sony Open with an even bigger win on Tuesday. The 24-year-old from Japan saved four match points to knock out the defending finalist, No. 4 David Ferrer, 7-6 (7), 2-6, 7-6 (9) in more than three hours.

Ranked No. 21, Nishikori has enjoyed a strong start to the season. He made the semifinals of the Brisbane International and played a great match against Rafael Nadal at the Australian Open before losing  7-6 (3), 7-5, 7-6 (3). After helping Japan beat Canada to advance to the Davis Cup quarterfinals, Nishikori won the U.S. National Indoor Tennis Championships for his fourth title.

But his best and most courageous tennis of the year has come over the last week in Miami. His 7-6 (1), 7-5 win over Dimitrov would have validated his tournament alone, but against Ferrer he overcame his nerves and took advantage of an under-prepared opponent (the Spaniard retired from the Mexican Open and missed the BNP Paribas Open with an upper-leg injury) to gut out his fourth win against a top-five player and make his first quarterfinal in Miami. Florida has been kind before to the Bollettieri-trained Nishikori, who won his first title just an hour up the road in Delray Beach in 2008.

Nishikori will face Roger Federer next. Regardless of the result, Nishikori will return to the top 20 on Monday.