The young driver, who celebrated his 22nd birthday on Saturday, is 29 seconds ahead of Frenchman Sébastien Ogier (Toyota) and 46 seconds and 4/10 over Estonian Ott Tänak (Hyundai), his runner-up in the world rankings.
The Finn, 4th at the end of the second day, gave himself his own gift for his birthday, taking the lead of the rally after his victory on the 9th special, before widening the gap by also winning the 11th and 12th special.
He could win his first world title on Sunday, during the Power Stage (a special which can earn up to five bonus points in the championship).
Rally leader after day two, Tänak suffered several time penalties for breaches of the hybrid engine rules, and fell behind Rovanperä on each stage, dropping two places in the standings.
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Contested in very rainy conditions, Saturday's specials were marked by several retirements, including those of the Briton Elfyn Evans (Toyota), second after the day on Friday, and Gus Greensmith (M-Sport Ford).
The Ford Puma of the latter and his Swedish co-driver Jonas Andersson rolled over on SS 10, the last of Saturday morning, coming to rest in a dangerous position for the competitors, but leaving the crew unscathed.
The 10th special was interrupted and then finally canceled for safety reasons.
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These retirements benefited Thierry Neuville (Hyundai), only sixth on Friday and now fourth.
The Belgian, third in the world championship standings, is however 1 min 41s and 4/10 seconds behind Rovanperä.
The final four stages of the rally will take place on Sunday, and could see Rovanperä become the youngest world rally champion in history.
© 2022 AFP