"Being away just the two of us and winning... It doesn't get much better than that," Roy said in a team press release.
It was an aggressive race with several early but unsuccessful breakaways, until Roy cleared the field over the Muur van Geraardsbergen.
A chase group of seven riders formed that included Elvin and Georgia Williams, but they were not able to close the gap to Roy. Elvin attacked that group on the Bosberg climb and bridged to her teammate, and the pair stayed away over the last 75km.
"That was such a cool way to win a bike race. We had a plan to be aggressive in Geraardsbergen, so the whole team was setting the pace on the front and when we hit the Muur I just slipped off the front with Gracie and Georgia in the chase behind," Roy said.
"Gracie attacked on the Bosberg and came across to me. We had a long way to go, and on a lumpy course, but we both felt good today and knew we had Georgia behind."
Their gap reached a maximum of three minutes with just 10km to go, and the pair crossed the line in Gooik hand-in-hand, as Roy took the win and Elvin placed second.
"It doesn't happen very often that you can win like this, so we can enjoy it," Elvin said. "Roy was strong and got away after the Muur. I then saw a good moment to attack to try to keep the move away, and nobody came with me, so I rode across to Roy and it worked.
"It definitely hurt, like a two-up time trial, and it wasn't exactly the plan, but it was really nice to win like this. It was so special and really cool. It feels like a big win."
Mitchelton-Scott have had a run of success as Amanda Spratt recently won the Emakumeen Bira Women's WorldTour race, while her teammate Annemiek Van Vleuten was second.
On the men's team, Mitchelton-Scott won five stages of the recently concluded Giro d'Italia. Esteban Chaves and Mikel Nieve won a stage each, and Simon Yates won three and led the race overall for 13 stages. The team also won all three stages of the Hammer Stavanger: Climb, Sprint and Chase.