Clement, runner-up at the 2001 Australian Open, caught Hewitt cold in the first set but the Australian world number three, playing in his home town, regained his composure to win the next two comfortably.
"I was probably trying to be a little bit too aggressive. I didn't serve well enough in the first set," Hewitt told reporters.
"I
Hewitt's biggest danger for the title, second-seeded Swede Joachim Johansson, made an impressive start to the new season with a 6-2, 6-4 win over another local hope Marc Kimmich.
Argentina's Juan Ignacio Chela also served notice to the top two seeds by thrashing Sargis Sargsian of Armenia 6-1, 6-1 while big-serving Taylor Dent beat fellow American Robby Ginepri 6-1, 2-6, 6-2.