Belgian Van Aert and Frenchman Pacher broke away from the rest of the group 30km from the end and Van Aert outsprinted his rival to claim his third stage win of the race.
"It’s not too often that I can win when my family visits me on a race so it makes it extra special and really nice," said Van Aert.
"It was really my aim to be in the breakaway but I had a hard time on the first climb. I almost gave up but I gave it one more try just before the top."
Spaniard Marc Soler came third after winning a sprint against Belgian William Junior Lecerf and Juri Hollmann from Germany, just over two minutes behind Van Aert.
Australian Ben O'Connor, who finished 22nd, retained the overall lead.
There were no significant moves among the top contenders, as O'Connor maintained his lead of three minutes and 53 seconds over Slovenia's Primoz Roglic.
"In the end, it was the perfect scenario. It was a really hard start, it took a long time for the break to go. A lot of guys in the top 10 were interested in the breakaway so I think we did a good job today to control the start," O'Connor said.
"I think tomorrow, the finale will be a little more decisive. The final climb is a hard one so it will be interesting to see."
