The Thai, seeded seventh, had been leading 4-3 when Slovakian Hrbaty quit, suffering the after-effects of influenza in the heat.
In second round matches, Russia's Mikhail Youzhny followed up his victory over second seed Guillermo Coria by beating Dutch qualifier Dennis Van Scheppingen 6-4, 7-5 and 17-year-old Spaniard Rafael Nadal beat Olivier Rochus of Belgium 6-3, 7-5.
Jarkko Nieminen of Finland defeated Frenchman Gregory Carraz 7-6, 6-3, while Dutch eighth seed Sjeng Schalken was stretched to the limit by 2002 champion Fabrice Santoro before reaching the quarter-finals with a 5-7, 6-4, 6-4 win.
It was a spot of good fortune for Paradorn who had his work cut out against a form player. Hrbaty has won three titles already this year in Adelaide, Auckland and last week in Marseille.
Five of the eight seeds had already been beaten in first round action this week.
Hrbaty explained he had no choice but to withdraw.
"I was sick last week and had a temperature before the final (in Marseille).
"I came here and thought I would feel better. Yesterday I was practising and didn't run too much and felt okay, but today when I played I felt when I was running I was coughing too much and couldn't breathe and I didn't feel I could finish the match."
Paradorn was glad of the short match. "It's good not to try too hard because of the conditions," he said. "It's hot and it was difficult conditions out there, and although I'm used to the heat it was good to play just seven games.
"If he wasn't sick it would have been a tough match."
