The 6 1/2-furlong event is for Ontario-foaled three-year-old fillies.
Finishing second was 3-5 favorite Woodsmoke, who won last month's Alywow Stakes. The Mike Keogh trainee was a head in front of third-place finisher How Far is Heaven.
After the race, trainer Malcolm Pierce and jockey Eurico Rosa da Silva were in agreement that Mullins Beach is a better filly on the turf, a surface over which she is 2-for-3 in her career, but 2-for-2 at Woodbine.
"She's definitely (better). She flows on the turf. She has a very nice stride. I like her much more on the turf," said da Silva, who was also aboard for her maiden-breaking turf victory on August 31.
"We've always thought this was a little bit better filly on the grass than on any other surface," added Pierce. "I was surprised she broke in front, but she settled back nicely and waited for (Eurico Rosa da Silva) to make a move."
Even though his mount broke running, da Silva said he was able to keep her a couple of lengths off the pace (:45.53) until the stretch.
"My filly broke very sharp, but (Woodsmoke) came very quick outside. I let her go to the lead. She was the speed horse," explained da Silva, who won last month's Queen's Plate with Eye of the Leopard. "My filly ran relaxed. I was watching (Woodsmoke) closely. I had tons of horse. At any time she could be right there."
Da Silva, who won three of the first four races on Sunday, asked the daughter of Speightstown for run at the head of the lane.
"When we turned home, I slowly moved her and she gave everything she had," he said. "She's a very nice filly."
Mullins Beach raced once at the Fair Grounds this winter before returning to Woodbine and scoring in the opening day feature, the La Voyageuse Stakes. She was third in the seven-furlong Fury but had been absent since the May 3 contest.
"After one of her breezes, she pulled up a little sore in one shoulder," explained Pierce, who has now won five added-money races at Woodbine this season. "She pulled a muscle or something. We missed a little bit of time, but it was probably a blessing in disguise. We waited for this race."
Mullins Beach is now a two-time stakes winner with a record of 4-for-8 and $255,220.
Ontario Racing Commissions reviewed the stretch run with regards to Woodsmoke and How Far is Heaven, but there was no change in the order of the finish.
Mullins Beach returned $8.40 and $3.40, combining with Woodsmoke ($2.50) for an exactor worth $19.60. How Far is Heaven rounded out a triactor worth $70.80. There was no show wagering.