Three-time Madrid Open champion Roger Federer was unable to save a crucial break-point in the first set on Thursday and went on to suffer an upset loss in the third round to 14th-seeded Kei Nishikori at the clay-court event, 6-4, 1-6, 6-2.
Federer, who entered the men's draw this week as the No. 2 seed behind world No. 1 Novak Djokovic, was the defending champion after winning on the controversial blue clay in Madrid a year ago.
The victory is a huge one for the 23-year-old Nishikori, who's the top-ranked men's player from Japan at No. 16 in the world. He has won just three singles titles thus far in his brief tennis career, but never on clay.
With the win, Nishikori advances to the quarterfinals on Friday, where he'll take on wild card Pablo Andujar for a berth in Saturday's semifinal round and a potential matchup with two-time Madrid Open winner Rafael Nadal.
Nishikori was previously 0-1 against Federer, falling to him in straight sets on the indoor hard courts in Basel in November 2011.
For the 31-year-old Federer, the loss is a setback in his effort to pick up some valuable points in the world rankings and hardly the ideal way to begin the European clay-court season.
The 17-time Grand Slam champion was making his return to competitive action following a two-month layoff after a disappointing loss to Rafael Nadal at Indian Wells last March. Based on previous seasons, Fed will likely play next week in Rome before gearing up for the French Open at Roland Garros later this month.
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