World number one Roger Federer questioned his decision-making after a shock 3-6 6-3 7-6(4) defeat by Australian Thanasi Kokkinakis in the Miami Open second round on Saturday.
It was the second loss in six days for the Swiss, who was beaten by Juan Martin del Potro in the Indian Wells final and is set to lose his top ranking to Rafa Nadal even though the Spaniard is not playing in Miami.
Kokkinakis, ranked 175th in the world, used a vicious top-spin forehand to wear down the defending champion and claim an upset victory in front of a stunned near-capacity crowd.
"Honestly, in the third set anything could have happened," Federer told reporters.
"The ball, I wasn't feeling. With my movement, things weren't absolutely working.
"I felt like the third could be a tricky one, of course. I feel like every time I had chances, something bad happened for me, wrong decision making by me, good decision making by him.
"Who knows what happened? It just felt like I could be paying the price for opportunities missed."
After the loss, Federer also announced his decision to skip the upcoming European clay court season, including the French Open.
"I decided not to play," Federer said of his plans for Europe.
The decision means the 36-year-old will follow the same path as last year, when he also took two months off after the Miami Open, before returning to win Wimbledon.
Kokkinakis is the lowest-ranked player to defeat a men's world number one since 178th-ranked Francisco Clavet beat Lleyton Hewitt in Miami 2003.
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