For the Glitterman filly, the seven-furlong event for Ontario-foaled fillies and mares was the first added-money tally of her career.
Glitter Rox finished one length in front of Dance to My Tune, who nosed out Half Sister for the runner-up position.
Jockey Chantal Sutherland was thrilled with the performance of the four-year-old filly, who is owned by Ellie Boje Farm, Peters, Read, Jean and Jim MacLennan.
"She's a little quirky. Every time she comes down the stretch, she looks at that grandstand," said Sutherland. "Today, I was waiting as long as I could to get to the front. She got there a little sooner than I had hoped, but I was ecstatic to win."
Glitter Rox entered the Belle Geste off a six-week layoff. Black said he had intended to race the filly in the Royal North Stakes on August 2.
"I had a minor setback before the Royal North. To get her a stakes win today is very good," he said.
Despite a serious injury early in her career, the homebred filly is now 5-for-14 with $271,162 in earnings.
"As a two-year-old, she flipped in the paddock and cracked her withers. We were surprised she ever came back from that," said Black.
Glitter Rox returned $6.50, $3.70 and $2.60, combining with Dance to My Tune ($4.20, $3.50) for a $30.30 exactor. Half Sister ($3.70) rounded out a triactor worth $153.40. Fourth-place finisher Septieme Vague completed a $1 superfecta worth $615.25.
Quiet Action and Becky Sharp were scratched.