Neuville completed the rally's first loop of gravel stages with a slender 2.0s advantage ahead of overnight leader Rovanpera, who impressed despite starting first on the road.
Toyota's Sebastien Ogier, on his WRC return, reached the morning tyre fitting zone in third (+4.6s) ahead of M-Sport's Ott Tanak (+8.3), with title contender Elfyn Evans in fifth, 12.5s adrift.
Hyundai's Esapekka Lappi (+14.0s) and Dani Sordo (+15.7s), followed by Toyota's Takamoto Katsuta (+18.3s) rounded out the top eight, while M-Sport's Pierre-Louis Loubet retired before tackling the day's opening stage.
The opening stage of the day was held in surprisingly dry conditions considering the deluge that Storm Daniel delivered prior to the rally start. Officials elected to shorten the stage by 7.5kms on Thursday night due to the heavy rain and floods that had damaged a section of the gravel stage.
Crews had expected far wetter conditions but were greeted by a relatively dry road, although the rain had exposed plenty of rough bedrock. It was bad news for overnight leader Rovanpera, who started first on the road.
The Finn was able to limit the effects of road cleaning to post the fifth fastest time on the test, 5.5s adrift of the pace, but he dropped to fourth overall.
After the cancellation of Thursday's Lamia shakedown stage, it was Neuville who appeared to have made the best gamble on set-up as the Belgian won the 10.37km Loutraki test by 3.4s from Ogier.
"We need to work a bit on the car, without shakedown there's a few small adjustments to do," said Neuville.
Source: Autosport