He began the day's final tests with a slender 2.4-second advantage over Mikko Hirvonen, who received a notional time for the stage prior to the interval, which was neutralised after M-Sport team-mate Ott Tanak caused a road block.
Ogier won again after the interval - giving the Volkswagen Polo R WRC its 200th stage win since its debut on the 2013 Monte Carlo Rally - before going on to complete a hat-trick of stage victories, while rally rival Hirvonen suffered tyre issues.
The Finn struggled all afternoon, complaining of a lack of grip as his rear tyres began to wear down to the canvas, and he subsequently lost 7.4s, 11.0s and 17.3s to Ogier.
Ogier retakes lead from Hirvonen
"They're completely gone," exclaimed Hirvonen. "Ogier's just running away and I can't do anything about it!"
Ostberg also struggled to keep up with the ultimate pace set by the reigning champion, but is still on the brink of a podium finish.
The Norwegian's nearest threat continues to be Dani Sordo, who rued running on soft compound tyres this afternoon, but was still able to maintain the 20-second deficit to Ostberg.
Henning Solberg entered the top five for the first time this weekend when Thierry Neuville lost more than six minutes in total after suffering a left-hand rear puncture and suspension damage on the penultimate stage of the day.
The Hyundai driver then had to nurse his poorly i20 through the final 22.15km test and he now lies 7m21.4s behind Ogier in seventh place.
Rally of Portugal seeks new location
Ogier takes dominant Portugal win