Loeb started Friday leading Hirvonen by just one second, but then went off and damaged his Citroen on the first stage of the day. The world champion reckoned a misjudged pace note led to the crash.
That left Hirvonen leading by 15s over Ford's Petter Solberg. As tyre wear became a major issue through the morning, Hirvonen was able to start edging clear, bringing his lead up to 25.8s after SS5.
Hirvonen and Solberg are the only frontrunners still in contention.
Already on the back foot after his Thursday delays, Jari-Matti Latvala then crashed on stage four, damaging his Ford's radiator and having to retire.
Thierry Neuville went off on the same stage as Loeb, ending his podium challenge. The Citroen Junior driver managed to get his DS3 upright again - injuring his hands in the process - but the engine had lost too much oil and he had to stop on the following road section.
Although Mads Ostberg is currently third in the Adapta Ford, he has been badly hampered by tyre wear and what he suspected was a further problem with the car. He is now only 7s ahead of the flying Evgeny Novikov.
Novikov looked like he was on course for a stage win on Tergu-Osilo, until being deposed by a remarkable performance from Sebastien Ogier in Volkswagen's S2000 Skoda.
Ogier holds seventh overall, behind Ott Tanak and Chris Atkinson, and just ahead of team-mate Andreas Mikkelsen.
Showing how much better the S2000 cars were handling tyre wear, Karl Kruuda was third quickest on SS5.
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- Petter Solberg