Nadal won 6-3, 6-4, 6-3 in just under 2½ hours Saturday in a match between former No. 1 players.
It was in the fourth round last year that Nadal's record 31-match winning streak at Roland Garros ended when he was upset by Robin Soldering. This year, the Spaniard will face No. 24 Thomaz Bellucci of Brazil at that stage.
Nadal is attempting to become the second man to win five French Open titles; Bjorn Borg holds the record of six.
This was the 10th meeting between Nadal and Hewitt. Nadal leads 6-4, having won their last five matches and eliminated Hewitt at the French Open in four of the past five years.