Nadal completed a career Grand Slam at the US Open last month
World number one Rafael Nadal beat Canadian qualifier Milos Raonic 6-4 6-4 to reach the quarter-finals of the Japan Open in Tokyo.
Spaniard Nadal will next play Russia's Dmitry Tursunov, who beat Frenchman Richard Gasquet on Wednesday.
American second seed Andy Roddick beat Jeremy Chardy 6-4 7-6 (7-4) to set up a quarter-final clash with number five seed Gael Monfils.
Frenchman Monfils beat Italy's Andreas Seppi 6-4 6-4.
"I converted both of my break points which is what you have to do against a big server," said Nadal. "I'm fresh mentally and that is sometimes not so easy this late in the season."
Roddick, who was knocked out in the second round of the US Open last month, said: "I'm at a point now where I'm not afraid to play long points any more.
"I haven't played much and I've struggled a little but it's nice not having to fight that mental battle. I played the big points very well. When you're playing average that's encouraging."
In other matches, Serbia's Viktor Troicki beat fourth seed Juergen Melzer 7-6 (9-7) 3-6 7-6 (7-3) to set up a quarter-final with last week's surprise Bangkok winner Guillermo Garcia-Lopez of Spain.