The SKODA Motorsport driver was half a second faster than Mikkelsen, bringing the gap between the two to 4.7 seconds overall.
“There was a lot of gravel on the road so it was difficult but there were no mistakes,” said the Finn, IRC champion in 2010.
Defending champion Mikkelsen, in a ŠKODA UK-backed Fabia, said: “There was more gravel but we tried to push. Juho is driving fast and there is not much I can do.”
Jan Kopecký was third fastest in his works Fabia.
He said: “It was not an easy stage and we are trying to stay on the road.”
Irishman Craig Breen has reduced the gap between himself and fifth-placed countryman Robert Barrable to 7.1 seconds after recording the fourth-quickest time in his Saintéloc Racing Peugeot 207 S2000.
French star Mathieu Arzeno was fifth fastest, and said: “It was slippery and difficult but when I look at the time of the ŠKODA drivers it’s unbelievable.”
IRC 2WD Cup leader Marty McCormack who suffered two right-side punctures in a stage to forget for the Ulsterman.