The 44th-ranked Collins was playing in her first career final while her opponent was aiming for her second title in two weeks.
The 27-year-old American lost a three-set quarterfinal to Ruse two weeks ago in Hamburg, where the Romanian went on to win as a qualifier.
Collins, who did not drop a set at the tournament, is the 14th first-time singles champion so far this WTA season. She has been playing regularly on the WTA Tour since 2018.
"It's given me so much self-confidence to finally win a tournament, because I've been on tour now for a couple of years, and that was one of my goals," Collins said on the WTA Tour website.
Ruse needed a medical time-out at 2-2 in the second set, but later fought off three break points at 3-2. But Collins converted her fourth break point of that game with a backhand crosscourt winner that nicked the sideline.
At 5-2, another return winner gave Collins her first championship point, and the American converted that chance.
"I've been improving, clearly, based on my results and being able to go longer with my stamina throughout the events," Collins said. "That was my main goal in playing all of the tournaments the last four weeks. It was just really rewarding to think about."