Top seed David Ferrer began the defence of his Japan Open title with a 6-4, 4-6, 6-1 victory over American Jesse Levine on Wednesday.
Second seed Andy Roddick also advanced to the last 16 of the of the $969,000 Tokyo tournament but the big-serving American was pushed to the limit in a 7-6, 6-7, 7-6 win over Czech Ivo Minar.
Chasing a place at the season-ending Tennis Masters Cup in Shanghai, world number five Ferrer recovered from a poor second set to finish off the second-round match in clinical fashion.
"I don't care about Shanghai right now," shrugged the Spaniard, who suffered an embarrassing opening match exit in Beijing last week.
"I'm just focusing on this tournament. I have three more tournaments before Shanghai. It's another week. What is important for me is to play well and take more confidence with me."
Ferrer's superior class showed in the deciding set as he buried Levine in a flurry of huge ground strokes, closing out the match with an ace to book his place in the last 16.
Ferrer will play Takao Suzuki next after the Japanese player upset Italian 15th seed Simone Bolelli 7-6 4-6 7-6.
Roddick, who like Ferrer is closing in on a place in next month's eight-man Shanghai shoot-out, struggled in his opening match three days after winning his 26th career title in Beijing.
The former US Open champion wasted three match points against Minar before coming through a third tiebreak 7-2 after more than two and a half hours.
Japan's number one Kei Nishikori delighted the home crowd with a 6-4, 6-4 victory over 16th-seeded Guillermo Garcia-Lopez of Spain.
The 18-year-old Nishikori, who earlier this year became the first Japanese player to win an ATP Tour title in 16 years, will face Frenchman Richard Gasquet for a quarter-final place.
"That was one of my best matches of the year," said Nishikori, ranked 84th in the world. "I like playing against seeded players so bring them on!"
Fourth seed Gasquet easily beat Austrian qualifier Martin Slanar 6-4, 6-2.
French seventh seed Jo-Wilfried Tsonga, this year's Australian Open runner-up who won his first tour title in Bangkok at the weekend, beat American Bobby Reynolds 4-6, 7-6, 6-4.
Spanish sixth seed Tommy Robredo beat Australian Joseph Sirianni 6-2, 6-2 to set up a meeting with ninth-seeded Czech Tomas Berdych.