Kei Nishikori eased into the quarter-finals of the Japan Open with a routine straight-sets win over Sam Querrey on Wednesday.

The defending champion and second seed is seeking to win the ATP 500 event for a third time and remains on course to do so following a 7-6 (7-3) 6-3 victory, marking his 50th of the season.

Nishikori won five of the first six points in a tie-break to take the first set and broke Querrey in third game of the second before comfortably closing the match out with a second break to set up a potential last-eight meeting with Marin Cilic.

Cilic was severely tested by Donald Young in the first round, but eventually came through 7-5 5-7 6-4 after two hours and 39 minutes.

"He was playing really well," Cilic said of his American opponent. "It was windy and I struggled with my serve in the third set."

Stan Wawrinka also required three sets to win in his second-round match, defeating home hope Tatsuma Ito 6-3 2-6 6-4.

The top seed's solitary break in the opener was enough for a one-set lead, but the resilient Ito fought back brilliantly to force a decider.

However, French Open champion Wawrinka raced into a 4-0 lead in the third and, despite dropping serve in the sixth game of the set, sealed his spot in the quarters.

Third seed Gilles Simon beat Jiri Vesely 6-4 6-2 and will take on Gilles Muller in the last eight following his 7-6 (7-3) 7-6 (7-5) defeat of Jeremy Chardy.

There was one surprise in Tokyo as Joao Sousa overcame seventh seed Feliciano Lopez 6-4 4-6 6-1 in the first round.