Kei Nishikori of Japan hits a return against Sam Querrey of the US during their second-round match at the Japan Open in Tokyo on Wednesday. Photo: AFP

Defending champion Kei Nishikori toppled giant American Sam Querrey 7-6, 6-3 to reach the quarterfinals of the Japan Open on Wednesday despite failing to really catch fire.

Second seed Nishikori, who was dazzling in canary-yellow shirt, headband and sneakers, struggled with a swirling wind in the early skirmishes in Tokyo before discovering his mojo in the first-set tiebreak.

He raced through it 7-3 after a ­dipping forehand forced the 1.98-meter Querrey into a wild miss.

Nishikori then secured an early break in the second set with an exquisite drop shot to afford himself the breathing space required to truly find his range.

The homegrown talent finished in style, belting a backhand down the line to set up match point and plunging home the dagger with an acrobatic smash. He celebrated with a pump of the fist and a toothy grin at coach ­Michael Chang.

"It was very important to keep my focus against such a big server," said Nishikori, who is bidding to win a third Japan Open in four years and next faces Croatia's Marin Cilic, the player who beat him in the 2014 US Open final.

"The first-set tiebreak was key," added Nishikori, chasing a fourth title of the year and the 11th of his career.

"After that I was able to relax a ­little and I think I played some pretty ­decent tennis. But I know it's going to get much tougher from here."

French Open champion Stan ­Wawrinka is also likely to provide a stern test to Nishikori's championship ­credentials this week. The Swiss top seed defeated Japan's Tatsuma Ito 6-3, 2-6, 6-4 in Wednesday's late match.

Third seed Gilles Simon blew past Czech Jiri Vesely 6-4, 6-2 to reach the last eight.

"It's a very tough tournament to win," the Frenchman told AFP of an event won in the past by such luminaries as John McEnroe, Ivan Lendl, Pete Sampras, Stefan Edberg and R­oger Federer.

"It's not one you win by chance. Each time the winner had been in the top 10 or not far outside. It would be a great achievement but you need to be playing at a really high level."

Seventh seed Feliciano Lopez from Spain had nothing left in the tank ­after reaching last week's final in ­Kuala Lumpur and was dumped out 6-4, 4-6, 6-1 by Portugal's Joao Sousa in a first-round match.

Sixth seed Cilic won his opener against American Donald Young 7-5, 5-7, 6-4, while Luxembourg's Gilles Muller beat Frenchman Jeremy ­Chardy 7-6, 7-6 to set up a quarterfinal against Simon.