Kuerten rolled to a 6-2, 6-4 victory against Bohdan Ulihrach of the Czech Republic while the second-seeded Hewitt was ousted by Nicolas Lapentti of Ecuador, 4-6, 6-4, 6-4. Both players received first-round byes.
Kuerten halted a five-match losing streak and improved to 5-1 against Ulihrach. The Brazilian is trying to pull a sweep of Paris titles after taking the French Open this summer.
The victory allowed the top-seeded Kuerten to open a lead of 133 points over Hewitt, who needs to win the Tennis Masters Cup in November to have a chance to overtake the top spot.
While Kuerten leads the ATP with six titles in 2001, Hewitt was on a roll before Tuesday's setback since winning his first career Grand Slam at the U.S. Open.
The 20-year-old Australian also helped his country to the Davis Cup final for the second straight year with a pair of singles victories.
He captured his fifth title of the year at the Japan Open and reached the semifinals at the Tennis Masters Series event in Stuttgart two weeks ago.
In other second-round matches, No. 3 Juan Carlos Ferrero of Spain advanced with a 6-3, 6-4 win over countryman Albert Portas. Belgian qualifier Christophe Rochus eliminated ninth seed Alex Corretja of Spain, 5-7, 7-6 (7-1), 6-4.
Wimbledon champion and No. 12 seed Goran Ivanisevic of Croatia also was upset, losing to Sweden's Andreas Vinciguerra, 6-4, 3-6, 7-6 (8-6).
Six first-round matches also were completed Tuesday. Albert Costa of Spain defeated French wild card Michael Llodra, 7-6 (7-3), 6-1, and Slovakian Dominik Hrbaty held off Belarussian Max Mirnyi, 6-2, 7-6 (7-4).
Also, Frenchman Julien Boutter was winning, 6-4, 3-1, against Andrei Pavel when the Romanian retired with an injury; Sjeng Schalken of the Netherlands had no trouble against Italian qualifier Frederico Luzzi, 6-4, 6-2; Ivan Ljubicic of Croatia beat Carlos Moya of Spain, 7-5, 6-1; and 1996 champion Thomas Enqvist of Sweden eased by Frenchman Nicolas Escude, 6-2, 6-3.