Top seed Roger Federer suffered a shocking early defeat as he was stunned 3-6, 6-3, 7-6(4) by world number 175 Thanasi Kokkinakis.
21-year-old Kokkinakis recorded the biggest victory of his career, in what also was a landmark victory, putting two years of injury problems behind him to become the lowest ranked player to beat a world No. 1 since Francisco Clavet (world No 178) beat Lleyton Hewitt in Miami in 2003.
Federer, a three-time champion in Miami, has not suffered defeat this early in Key Biscayne since 2000 when as an unseeded teenager he was beaten by Mariano Zabaleta.
“It’s disappointing.” Federer said. “Don’t know why but I could never get to any level that I was happy with today. Sometimes you have these matches.
“Sometimes you find a way through. I just couldn’t get it done today. He was just a bit better than me today, you know.”
Federer’s early defeat means Rafael Nadal will reclaim the ATP number one ranking when the updated standings are released next Monday.
Kokkinakis will now face Fernando Verdasco in the third round.
In the women’s field, world number one Simona Halep failed to make it past the third round as she was bundled out by Agnieszka Radwanska.
Radwanska, ranked 30, bounced back from a first set loss to win 3-6, 6-2, 6-3, handing Halep her first ever defeat in Miami to a player ranked outside the Top 20.
The victory is Radwanska’s second career win over a World No.1, and the first since 2012. She will now take on Victoria Azarenka for a place in the quarterfinals.