MIAMI (AFP) - Two-time Grand Slam champions Stan Wawrinka and Petra Kvitova crashed out of the ATP and WTA Miami Open on Saturday while Japanese sixth seed Kei Nishikori was tested but advanced.
Swiss fourth seed Wawrinka, who has won titles this year at Chennai and Dubai, was ousted by Russia's Andrey Kuznetsov 6-4, 6-3 while Czech eighth seed Kvitova, the 2011 and 2014 Wimbledon winner, fell to Russian 30th seed Ekaterina Makarova 6-4, 6-4.
"I just tried to keep the pressure on him," said Kuznetsov, who fired 23 winners and seven aces to advance in 79 minutes.
Wawrinka, the 2014 Australian Open and 2015 French Open champion, managed only 16 winners against 37 unforced errors and went 0-for-8 on break point chances.
Kuznetsov, ranked a career-best 51st, avenged a third-round loss to Wawrinka earlier this month at Indian Wells and made the Swiss his highest-ranked beaten foe, surpassing seventh-rated Spaniard David Ferrer from the second round of Wimbledon in 2014.
Spanish fifth seed Rafael Nadal, a four-time finalist but never a champion at Miami, is now the top seed in his quarter of the draw. The 14-time Grand Slam champion opened later against Bosnia and Herzegovina's 94th-ranked Damir Dzumhur.
Nishikori advanced to the third round by defeating 107th-ranked French qualifier Pierre-Hugues Herbert 6-2, 7-6 (7/4).
The 26-year-old Asian star, runner-up at the 2014 US Open and coming off a fourth consecutive title last month at Memphis, denied the Frenchman on two set points in the ninth game of the second set and took four of the last five points in the tie-breaker to win after 88 minutes.
"He played much better in the second set," Nishikori said. "I tried to be aggressive. I knew I had to somehow give him some pressure. I stayed confident even a break down and had a good win."
Next up for Nishikori, who could meet Britain's Andy Murray in a quarter-final, is Ukraine's 27th-seeded Alexandr Dolgopolov, a 6-4, 6-4 winner over Italy's Andreas Seppi.
Nishikori broke twice at the start to seize a 4-0 lead and took the first set in 29 minutes, but Herbert hit a forehand crosscourt winner to break Nishikori for a 3-1 lead in the second.
Herbert served for the set up 5-3 but squandered two set points, Nishikori hitting a forehand lob winner and Herbert sending a backhand wide before the Frenchman double faulted away a break.
In the tie-breaker, Nishikori sent a backhand long to level matters at 3-3 but dominated from there and finished on a service winner.
Canadian 12th seed Milos Raonic, coming off a runner-up showing at Indian Wells, beat American Denis Kudla 7-6 (7/4), 6-4. He next faces US 22nd seed Jack Sock, who advanced 6-2, 3-2 when Ukraine's Sergiy Stakhovsky retired.
Polish third seed Agnieszka Radwanska reached the last 16 by beating American Madison Brengle 6-3, 6-2.
World number one Serena Williams will try to reach the fourth round while second seed Murray open his title quest later at the hardcourt event.
Three-time defending champion Williams, coming off back-to-back finals losses for the first time since 2004 at the Australian Open and Indian Wells, meets 97th-ranked Kazak Zarina Diyas.
The US star, a 21-time Slam winner and eight-time Miami champion, struggled in her three-set opening win over compatriot Christina McHale.
If Williams advances, and she has never failed to reach the last 16 at Miami, she would next face Russian 15th seed Svetlana Kuznetsova, who outlasted France's 48th-ranked Caroline Garcia 4-6, 6-2, 7-6 (8/6). Williams is 8-2 all-time against Kuznetsova, winning their most recent match in last year's Miami fourth round.
Murray, the 2012 US Open and 2013 Wimbledon champion, faces Uzbekistan's Denis Istomin, whom he beat twice in 2013 in their only prior meetings. The Scotsman won the Miami crown in 2009 and 2013 and was runner-up to Novak Djokovic in 2012 and 2015.