Playing her first WTA tournament of the year, Safina took advantage of five double faults by Cirstea to advance to the second round after the 58-minute match at Ken Rosewall Arena in Sydney.
Safina said despite the score, Cirstea had pushed her to play aggressively.
"She goes for the shots, so I had to avoid this," Safina said. "I had to be much more aggressive, as she is. I think I did this pretty well today."
Safina said she appreciated the pre-Grand Slam practice she was getting at the Hopman Cup and Sydney. The Australian Open begins on Monday in Melbourne.
"You have to try the things you've been working on" in the off-season, she said. "Now I've played many matches and I still feel that I can improve." Safina has nine WTA singles victories.
In other matches, Alize Cornet of France beat No. 7 Nadia Petrova of Russia 6-2, 6-4 and eighth-seeded Caroline Wozniacki of Denmark defeated Dominika Cibulkova of Slovakia 6-1, 6-2.
Sara Errani beat Casey Dellacqua of Australia 6-1, 6-2.
No. 4 Vera Zvonareva of Russia withdrew with a stomach ailment and Victoria Azarenka, who won the Brisbane International title on Saturday, pulled out of her first-round match with a virus.
Melanie Smith of Britain advanced to the second round when Marion Bartoli of France retired with a left calf muscle strain at 1-1 in the first set.
In first-round men's play at the joint ATP-WTA event, fifth-seeded Igor Andreev of Russia beat Canada's Frank Dancevic 7-6 (2), 6-3 and seventh-seeded Tommy Robredo of Spain, a former Australian Open quarterfinalist, defeated Austrian Jurgen Melzer 6-3, 6-4.
Michael Llodra of France defeated Denis Gremelmayr of Germany 6-0, 6-2 and Mario Ancic of Croatia beat Belgium's Xavier Malisse 4-6, 7-6 (5), 6-3. Jarkko Nieminen of Finland beat Feliciano Lopez of Spain 6-2, 7-6 (9) and Simone Bolelli of Italy defeated countryman Potito Starace 7-6 (1), 6-4.
In Hobart, Australia, No. 4 seed Zheng Ji of China defeated New Zealand's Marina Erakovic 6-1, 4-6, 6-1 at the Hobart International Monday.
Poland's Urszula Radwanska beat sixth-seeded Aleksandra Wozniak of Canada 3-6, 7-6 (3), 7-5.
Anne Keothavong of Britain beat fifth-seeded Agnes Szavay of Hungary 6-3, 7-5 and Carla Suarez Navarro of Spain ousted third-seeded Anna Chakvetadze of Russia, 7-6 (5), 1-6, 7-5.
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