Roy's triumph came over fellow escapees Evy Kuijpers (GRC Jan van Arckel) and Susanne Anderson (Norway) as the remainder of the lead group followed behind.
It's the fast woman's first win in Orica-AIS colours since joining the team in 2015.
.@Sar_Roy @ORICA_BE wins stage 4 @shertogenbosch. 2 @EvyKuijpers 3 @SuzanneAnderse. #BRLT16 pic.twitter.com/wKUwdg7TMc — Holland Ladies Tour (@ladiestour) September 2, 2016
"I'm pretty excited to have won today it's my first win for Orica-AIS and we had some great team work out there with Taylor Wiles and myself in the breakaway for the majority of the race," 30-year-old Roy said.
"We got about four to five minutes from the peloton and it was a good combination of riders. We were very lucky to stay away and the peloton let us stay out there.
"It got pretty aggressive out there towards the end a lot of attacks a lot of chasing and Taylor and I worked so well together. She really put the pressure on at the finish there I timed my sprint perfectly so I was really lucky.
I've worked a lot on my sprint this year. I've always been there or nearly been there. At the Route de France, I'd be second wheel coming in to the last 500 metres and I'd always make a big mistake. So it's really nice to take the win here and give myself a bit of confidence.
"And all the people that believe in me can tell me now that they told me so."
Boels-Dolmans rider Chantal Blaak remains in the leader's jersey.
As it happened
After a challenging stage 3 through rolling Dutch countryside, a flatter stage faced the peloton from the flag. But the attacks came thick, fast and early. Proceedings settled until 14 riders managed to pull clear after around 35 kilometres raced.
A group of 13 riders is trying for a breakaway. #BRLT16 pic.twitter.com/bzzeu2UKZ3 — Holland Ladies Tour (@ladiestour) September 2, 2016
The break comprised Roy, Wiles, Kuijpers, Andersen plus Barbara Guarischi (Canyon SRAM), Emma Johansson (Wiggle High 5), Jeanne Korevaar (Rabo Liv), Christine Majerus (Boels-Dolmans), Simona Frapporti, Emilie Moberg (Hitec) Riejanne Markus (Liv-Plantur), Natalie van Gogh, Janneke Ensing (Parkhotel Valkenburg), and Nina Kessler (Lensworld-Zannata).
With no one ahead threatening the GC, the peloton allowed the lead bunch some leeway. With 25 kilometres to go, their lead grew to a maximum of five minutes.
The 14 leaders with @EvyKuijpers @janvanarckel in the front. The gap is 5 min. 25 km to go. #BRLT16 pic.twitter.com/IKfseOCqzZ — Holland Ladies Tour (@ladiestour) September 2, 2016
Multiple attacks were deployed in the closing kilometres but ultimately it came down to a bunch sprint.
