Russian second seed Sharapova, who needs a Roland Garros title to complete a career Grand Slam, hardly broke sweat against her 22-year-old opponent who was so penniless in 2008 that she had to stop playing.
On Tuesday's evidence, it was easy to see why.
Sharapova, twice a semi-finalist in Paris, allowed the 78th-ranked Romanian just nine points in the opening set which was wrapped up in 23 minutes on Suzanne Lenglen court.
It was a similar tale in the second, with Sharapova again surrendering just nine points before wrapping up victory when Cadantu hit long with a forehand.
Sharapova unleashed 19 winners in her victory while the Romanian hit none at all.
The second seed will face Japan's Ayumi Morita for a place in the last 32.