Vandewalle finished eight seconds ahead of Radioshack Leopard's Tiago Machado, with his team-mate Gert Steegmans just a further second behind.
"It was great to win today, with it only being my fifth race of the season." Vandewalle said, before adding that his team's unusual warm-up gave him the edge.
"We started warming-up by pacing behind our bus driver Dirk Clarysse, which was 40km from the start. I think it was the right decision to do it like that."
The winner said that he was relieved even to be at the start line after falling ill recently.
"My condition was good for this race. But last week I became sick so it was one big question mark if I would be good today or not.
"So I had quite a good feeling when I started today, but did not come into this race expecting to have such a good result."
Vandewalle believes that his team will win more stages as the race continues over the next two days, with sprinter Mark Cavendish expected to contend.
"We will do our best to keep the leader's jersey in the team. Hopefully we can come into the next races with a win," he said.
"I think it can be two times a bunch sprint if the wind is not that strong in either stage. With a guy like Cavendish on the team we always have a good chance."