The Estonian driver won by 7.0 seconds after Toyota's overnight leader Sebastien Ogier crashed on the penultimate stage.
Tanak's second victory of the season, in a rally that started in Prague and used asphalt roads in Austria and Germany, cut Neuville's championship advantage to 25 points.
Neuville, who would have sealed his first WRC title on Sunday had he scored two points more than Tanak, finished third and 25.8 seconds behind Toyota's second-placed Elfyn Evans.
"It wasn't to be this weekend," said the Belgian, who had led on Friday night but dropped to fourth on Saturday after twice going off the road.
"Japan is coming up and looking forward to it."
Toyota cut Hyundai's lead in the manufacturers' championship to 15 points.
Japan's Takamoto Katsuta finished fourth for Toyota, and took five points from the final power stage, with Gregoire Munster fifth for M-Sport Ford.
Ogier lost the lead with an error on Sunday's opening stage and then ran wide into the trees.
"This first corner, this long corner under the trees, people were cutting more than anticipated and the corner became very muddy and greasy and I couldn't turn," said the eight-time world champion.
"So I understeered and hit the trees at the side."
Rally Japan runs from November 21st to 24th.