Hirvonen, third in the championship behind the Citroen pairing of Sebastien Loeb and Sebastien Ogier, won his home rally last year.
Norway's Petter Solberg, fastest on the opening stage, took over the lead in a privately-entered Citroen with Finland's Jari-Matti Latvala second for Ford and 1.3 seconds adrift after five stages.
Six-times world champion Loeb was in sixth place after damaging his car's front bumper in stage three.
"The car is undriveable. Every corner I try to steer, the car is going straight. I have to turn in on the brakes. The car is impossible to drive. I was surprised that the car was like that. Incredible, it's missing all the (aero) effects," Loeb told the autosport.com website.
(Writing by Alan Baldwin in Budapest; Editing by Clare Fallon)
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