Third-seeded Novak Djokovic was leading 6-2, 4-3 against Dmitry Tursunov when the Russian retired with an injured right shoulder, seventh-seeded Roddick beat Feliciano Lopez of Spain 6-3, 6-4, and ninth-seeded del Potro defeated Mario Ancic of Croatia 6-0, 6-4.
Also, 15th-seeded Fernando Verdasco outlasted Spanish countryman Tommy Robredo 6-2, 6-7 (6), 6-2, and 16th-seeded Gael Monfils topped Juan Monaco of Argentina 6-4, 6-4 to set up a possible match against top-ranked Rafael Nadal.
Tursunov retired against Djokovic after twice needing treatment on his shoulder. Djokovic, the Australian Open champion, hasn't won a title since his third of the year at the Rome Masters in May.
"Still trying to find my top form. Lately I've been struggling on the court,'' Djokovic said. "But still, I'm fighting. I know that I have to fight for every point and just find my best shape.''
Djokovic has never beyond the third round at the Paris Masters and next plays either No. 13 Jo-Wilfried Tsonga or 2004 runner-up Radek Stepanek in the third round.
"This time I'm motivated to do well and I have nothing to lose,'' Djokovic said.
Roddick has reached the Paris semifinals twice in his last three appearances.
"I felt like I hit the ball pretty well tonight,'' Roddick said. "You know, I wanted to try to hit it firm and deep, because anything short and he tries to get in on and then starts putting pressure on.''
He and del Potro are chasing the last three spots for the season-ending, eight-man Masters Cup in Shanghai. Roddick was sixth in the standings and del Potro seventh heading into this week's tournament at Bercy Indoor Arena.
Roddick refused to think ahead to Shanghai.
"I'm not going to talk about going to a tournament that I'm not even in yet,'' he said. "I think that's a little bit cocky, maybe a little bit arrogant to assume that you're going to make something.''
Del Potro, who unlike Roddick has never qualified, said, "I'm trying not to think about it. I always wake up thinking about Shanghai.''
Del Potro next faces eighth-seeded David Nalbandian of Argentina or Nicolas Kiefer of Germany. If Nalbandian, it will be their third match in three weeks, with a win apiece.
"I'm playing more aggressive now, I'm serving very well,'' del Potro said.
Del Potro, Roddick and Gilles Simon are looking to gain enough points to hold their places in the top eight for Shanghai. Simon, in the eighth spot, will play Igor Andreev in the second round on Wednesday. If he wins, Simon will face Roddick in the third round.
"He's definitely improved,'' Roddick said of Simon. "To kind of have his career-best year and to make a run late in the year, he's been winning a lot of close matches, which shows his confidence level.''
Monfils, meanwhile, was celebrating his first appearance in the Paris Masters third round.
"I wanted to do so well. Juan is a very good player, and he beat me twice already,'' Monfils said. "Thanks to my serve I was able to be more confident.''
In first-round action, new Lyon Grand Prix champion Robin Soderling won his sixth straight match against Josselin Ouanna of France 6-3, 6-4 to set up an eighth career meeting with Roger Federer.
Soderling was 0-7 against Federer, who won his 57th career title at the Swiss Indoors on Sunday.
Germany's Philipp Kohlschreiber beat Russia's Mikhail Youzhny 6-1, 6-4; 2005 runner-up Ivan Ljubicic of Croatia beat Viktor Troicki of Serbia 6-3, 6-4; and Stepanek of the Czech Republic downed Marc Gicquel of France 6-4, 3-6, 6-4, and Florent Serra beat Guillermo Canas of Argentina 4-6, 7-5, 6-3. Serra will meet Nadal next.
Ljubicic will play 2006 champion Nikolay Davydenko of Russia.
Kohlschreiber had to save eight break points, and next plays fifth-seeded David Ferrer of Spain.
Ferrer is just behind Simon in the race for Masters berths, with James Blake, Stanislas Wawrinka and Australian Open finalist Tsonga all hoping a good showing will help them qualify.
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