BELGRADE - Novak Djokovic has lost the killer instinct that enabled him to rule men's tennis for a number of years, former coach Niki Pilic said on Saturday.

"Djokovic reached the Mount Everest of tennis last year after winning the French Open," Pilic, who guided the Serb as a junior at his Munich academy, told Bosnian daily Nezavisne.

"He had 16,950 points and that's a tally that will never be repeated again. But loss of form and missing tournaments made his advantage melt away."

Djokovic looked untouchable after capturing his 12th grand slam title at Roland Garros last June, but was dethroned from the top of the world rankings last November by Andy Murray, who beat him in the final of the season-ending ATP World Tour Finals.

The 29-year-old Serb appeared to have rediscovered some of his form when he gained revenge over the Scot in January's Qatar Open final, but he then went down to a shocking second-round exit from the Australian Open at the hands of unheralded Denis Istomin.

Last week Djokovic was beaten by Australian Nick Kyrgios in the quarterfinals of an ATP event in Acapulco, prompting Pilic to cast doubts whether his former protege can regain top spot.

"Novak had a physical and mental edge second to none, he was in sixth gear," said the 77-year-old Croatian who helped a Djokovic-led Serbia to its 2010 Davis Cup title in an advisory role.

"That tenacity is no longer the same. It remains to be seen whether he can rediscover it and get back to the top level.

"The hard work of the past five or six years has taken its toll. Tennis was his priority every morning and afternoon and evening. All I can tell him is to be the person he was."

Nadal knocked off

Unseeded American Sam Querrey stunned second-seeded Rafael Nadal 6-3, 7-6 (3) to win the ATP Mexico Open on Saturday and end the Spaniard's run of perfection in Acapulco.

Querrey, ranked 40th in the world, fired 19 aces en route to his first career victory over Nadal in five meetings. The Spaniard, who won the event in 2005 and 2013, had never even lost a set in Acapulco.

Querrey captured his ninth ATP title in an impressive week that saw him beat four top-10 players - Belgian David Goffin, Austrian Dominic Thiem, Australian Nick Kyrgios and sixth-ranked Nadal.

Nadal, playing his first tournament since falling to Roger Federer in five sets in the Australian Open final, was denied his first hard court title since Doha in 2014.

Nadal, roared on by a supportive crowd, was seeking his 70th career victory and his third in Acapulco, though his first since the event moved from clay to hardcourt in 2014.

Reuters