Safin, a former top-ranked player and a three-time champion at the Paris tournament, wants a long break before making a decision.
"I don't know what happened. Just couldn't find my rhythm and couldn't find the game," the 28-year-old Russian said. "I need to think everything through. I have no pressure and I have nothing to prove or show. I just want to be comfortable with my decision, whatever I will take."
Safin managed only 12 points in the first set and trailed 2-0 in the second after just 24 minutes. In the first service game of the second set, Safin had four double faults before breaking back to 2-2.
"I need to sit down and relax and just enjoy my life without any tennis [for] a couple of months and then I will see," Safin said. "If I feel like I want to continue to play, I will. If not, it will be over."
Safin won the U.S. Open in 2000 and the Australian Open in 2005. He hasn't won a tour title since the victory in Australia.
"I've been struggling throughout my career with injuries left and right," said Safin, who is ranked 31st. "It's a little bit uncomfortable to find yourself in the top 10 for many years and to find yourself ranked 70 and 30 and 50 ... It's not really a comfortable position."
Berdych, the 2005 winner, eased past Robby Ginepri of the United States 6-4, 7-5, Cilic downed Andreas Seppi of Italy 7-6 (5), 6-2, and Kiefer beat big-serving Ivo Karlovic of Croatia 6-4, 7-5. Simone Bolelli beat Jarkko Nieminen 7-5, 6-4.
"He broke me twice, then he got a bit tired when he was serving for the set and I took advantage of that," Cilic said.
Sam Querrey of the United States advanced to a second-round match against fourth-seeded Andy Murray. The big-serving Querrey had secured a break in the third set and was leading 7-5, 6-7 (5), 3-2 when Marcos Baghdatis retired.
Baghdatis, a Paris semifinalist last year, quit after calling a trainer to massage his lower back. He had also pulled out during the second set against Karlovic at Metz on Sept. 30.
"I felt a sharp pain and I didn't want to take any risks," Baghdatis said. "I felt that if I continued, I would have had problems afterward. So I preferred to stop."
Mathieu was broken in the sixth game of the second set and never recovered. An ace brought up match point for Andreev and he wrapped up the match with a forehand pass that Mathieu returned into the net.
"This season ended very badly for me," Mathieu said. "I had a lot of hopes for the indoor season."
The three remaining spots for the season-ending Masters Cup will be decided this week, with Andy Roddick, Juan Martin del Potro and Gilles Simon each looking to gain enough points to hold their ranking in the top eight and reach Shanghai.
But David Ferrer is just behind Simon, with James Blake, Stanislas Wawrinka -- who next plays Berdych -- and Australian Open finalist Jo-Wilfried Tsonga all hoping a good showing will help them qualify for the prestigious year-end championship.
Roger Federer, who won the Swiss Indoors at Basel for the third straight year on Sunday, confirmed Monday to tournament organizers that he will play at Bercy despite feeling tired after beating David Nalbandian for his 57th career title.