Roddick claimed the sixth spot in the eight-man Masters Cup in Shanghai next month, leaving Juan Martin Del Potro and Gilles Simon waiting on Friday's results to see if they keep the last two berths.
Nadal beat Gael Monfils of France 6-3, 6-2, Federer defeated Marin Cilic of Croatia 6-3, 6-4, while Djokovic, the year's other major winner, lost to Jo-Wilfried Tsonga of France 6-4, 1-6, 6-3.
Nadal saved all nine break points he faced and broke Monfils three times, clinching victory on his first match point when the Frenchman hit a forehand wide.
"I'm not playing my best level, but I'm not playing badly," Nadal said. "If I can improve a bit for tomorrow and for Shanghai I think I can finish the year playing well."
Nadal will play Davydenko, who crushed 2005 champion Tomas Berdych of the Czech Republic 6-1, 6-1.
Even though Nadal was guaranteed to start 2009 ahead of Federer in the rankings, he feels like he's still behind him.
"Roger had four or five years with the No. 1, winning two, three Grand Slams a year," Nadal said. "So for that reason I think everybody says Federer is the best."
Nadal saved all nine break points he faced and broke Monfils three times, clinching victory on his first match point when the Frenchman hit a forehand wide.
Federer's fourth ace sealed a dominant victory against the 20-year-old Cilic, and allowed him to cast an eye on his first semifinals at Bercy Indoor Arena.
"I prefer to come back to a place where I had success in the past. This is not the case here," Federer said.
Copyright 2012 by STATS LLC and The Associated Press. Any commercial use or
distribution without the express written consent of STATS LLC and The
Associated Press is strictly prohibited.