With 16 stages to come over the next three days, the opening challenge of the race in Sardinia saw the field compete over a 1.3-kilometre course in Cagliari.
The short course saw the drivers go head-to-head in mini-heats around the city's port, and it was M-Sport World Rally driver Hirvonen who clocked the fastest time, beating Jari-Matti Latvala by 1.7 seconds in his heat.
"That was an okay stage," Hirvonen told the World Rally Championship's official website.
"It's good to get the rally started and I feel in a good place right now."
World champion Sebastien Ogier tied for second with Thierry Neuville, the duo finishing 0.2secs adrift of Hirvonen.
Juho Hanninen set the early pace with victory over Martin Prokop, but it was not long before Hyundai's Neuville moved top of the time sheets.
Neuville beat Citroen's Mads Ostberg but his lead lasted less than two minutes as Hirvonen eclipsed him.
Ogier was last to go in the opening stage but could not top Hirvonen's effort.
Hanninen finished fourth, while Citroen's Kris Meeke, who lost to Ogier, shared fifth with Latvala.
The drivers now prepare for a tough second day of the rally, with eight stages ahead of them on Friday.