The top eight were all given byes into the second round of the claycourt event.
Camerin had won only two matches in 12 tournaments before arriving in the Italian capital but mastered the blustery conditions to oust Frenchwoman Dechy, who reached the semi-finals of the Australian Open in January.
It was the first of a trio of Italian victories.
Thirteenth seed Silvia Farina Elia enjoyed a 6-4 6-1 win over Russia's Maria Kirilenko while the unseeded Francesca Schiavone defeated Meghann Shaughnessy of the U.S. 7-5 6-0 to set up a meeting with third seed Serena Williams.
"Everything is in her favour, from her ranking to her victories," Schiavone told reporters of her clash with the former world number one.
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"In my favour all I have is the crowd. I hope lots of people come and support me so I can play my best tennis."
Williams was in confident mood. The American has an excellent record in Rome and won the tournament in 2002.
"I'm not frightened of anyone. If anything, it's the other players that should be frightened of me," she said.
Asked whether she was already targeting the French Open in Paris which starts on May 23, Williams replied: "No, I'm not thinking about Roland Garros yet.
"I'm just taking one match at a time. The only thing that's important is that I go out on the court concentrated."
There were no problems for Elena Bovina, the highest-ranked player to appear on the opening day.
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Claycourter Anabel Medina Garrigues advanced to a second-round match against top seed Maria Sharapova by beating Alina Jidkova of Russia 6-4 6-1.
Sharapova can wrestle the world number one spot away from Lindsay Davenport by winning in Rome this week.
But having reached only two quarter-finals in her previous six claycourt events, the Russian teenager would be unwise to take Garrigues's challenge lightly.
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