Hyundai's Neuville goes into Sunday's finale with a narrow 4.9sec edge over Toyota's Elfyn Evans after the two title rivals were locked at the same time on Friday night.
Eight-time world champion Sebastien Ogier, in another Toyota, ended the day within 11.6sec of Neuville in third place.
"It's not a big lead, but we had a great day," said Neuville, now in his 10th season with Hyundai and who claimed victory in the season-opener in Monte Carlo.
"Despite a not perfect tyre choice this afternoon we were capable of defending our lead. We need to continue attacking and have a good tyre choice on Sunday. It wasn't easy when the weather wasn't very easy to judge."
Former world champion Ott Tanak was fourth, more than a minute off the lead in another Hyundai despite damaging a rear wheel when he ran wide and clipped a kerb.
Standings on Saturday:
1. Thierry Neuville/Martijn Wydaeghe (BEL/Hyundai): 2:09:46.0, 2. Elfyn Evans/Scott Martin (GBR/Toyota) at 4.9, 3. Sebastien Ogier/Vincent Landais (FRA/Toyota) 11.6, 4. Ott Tanak/Martin Jarveoja (EST/Hyundai) 1:15.5, 5. Adrien Fourmaux/Alexandre Coria (FRA/M-Sport Ford) 1:35.4
