"I wasn't great, I was so glad to win,'' Williams said. "As the tournament goes on, I'll do a little better.''
Williams fell ill after winning the Australian Open and wasn't able to practice until Monday.
"I was in bed, I was really sick until I came here,'' Williams said. "It was like a week. I could't do anything.''
Williams, who recently bought a flat in Paris, playfully answered in French some questions from the local press. "I feel so-so, I'm tired right now, I'd like to sleep,'' she told reporters in French.
The top-ranked Williams saved two break points on her first service game before winning six games in a row to take the first set on an unforced error from Benesova.
The 34th-ranked Czech fought back in the second set, but Williams won the match on Benesova's serve with a backhand winner down the line.
"She raised her game and I made some key errors on some key points (in the second set),'' Williams said.
Williams will next play Croatian qualifier Karolina Sprem.
Meanwhile, Patty Schnyder of Switzerland edged Alona Bondarenko of Ukraine 6-4, 7-6 (3).
Schnyder will meet French wild card Nathalie Dechy in the second round.
Jelena Jankovic of Serbia played Francesca Schiavone of Italy later on Wednesday while Elena Dementieva of Russia took on Aravane Rezai of France.
Karim Benzema Ready To Stay With Lyon
Serena Williams reaches 2nd round at Open GDF Suez
