Before he climbed aboard Dirt Road Queen in May, Seth Martinez had not ridden a quarter horse in five years. If the jockey had known the filly’s history, she might not have been the first choice for his return.

Dirt Road Queen didn’t even get to the gate in her first two attempted starts. Both times, the rowdy 2-year-old broke loose from her equine escort before she could be loaded, then dumped her rider and ran off. “I didn’t hear about how bad she was until I’d ridden her twice,” Martinez said. “Now, you’d never think she was anything like that.”

The reluctant racehorse of last year has matured into a model athlete, winning all four of her races this summer at Canterbury Park. Dirt Road Queen and Martinez will attempt to make it five-for-five when they run in Sunday’s Minnesota Quarter Horse Derby, part of Canterbury’s Festival of Champions for Minnesota-bred horses. Three of her victories have been in stakes races, fattening her season earnings to $44,865 and putting her in contention for the track’s horse of the year award.

The stout sorrel filly is as sweet as she is swift. Affectionate with everyone at trainer Bill Harris’ barn — including the young children of groom Tracie Aker — the horse known as “Princess” also found her form at an opportune time for owners Bob and Julie Petersen. Her success this summer has soothed their pain after the death of her half-brother Sportwagon, a rising star lost last spring.

Dirt Road Queen began the Canterbury meet with a reputation as an ill-mannered rogue. Though Harris and the Petersens knew better, they couldn’t have predicted how beautifully their filly would blossom.

“We thought she would be a nice mare, but I have to say we’re pleasantly surprised,” Harris said. “Now she loves what she’s doing, once she figured it out. She’s just kind of put it all together and grown into a racehorse.”

The Petersens have won nine Festival of Champions races, more than any other quarter horse owners. Dirt Road Queen represents a third generation of Petersen-bred runners at Canterbury Park, following her grandmother Inclined To Cash — the couple’s first racehorse — and her mother, Inclinda, the Minnesota Derby champion in 2002.

Inclinda was a late bloomer, a quality she passed to her daughter. Once Dirt Road Queen finally got into the starting gate last July, she didn’t show much, finishing third in her debut before running well back in the pack in two other races. The filly got some time off at the Petersens’ farm near Cokato, then Harris took over her training.

The group was heartbroken when Sportwagon, the winner of the Minnesota Quarter Horse Futurity on Festival day last year, cut his leg in the paddock and had to be euthanized when a severe infection set in. Dirt Road Queen’s progress helped lift their spirits. The first time Harris’s wife, Lori, galloped the filly, she gave a one-word review: Wow.

“We expected great things from Sportwagon, and that was hard to take,” Bob Petersen said. “But [Dirt Road Queen] picked it up. She was like a big kid last year; she just needed time to get on top of the game mentally. And then, she was ready to go.”

Dirt Road Queen broke her maiden in a claiming race May 25 with Martinez aboard. The pair followed up with victories in the Minnesota Stallion Breeders’ and NCQHRA Derby, the Bob Morehouse Stakes and the Cash Caravan Stakes.

The Petersens have won 79 races and more than $760,000 in purses at Canterbury, the most of any quarter horse owners in track history. The Festival of Champions always is a special day for them, Bob Petersen said, one that typically ends with a party at the barn. Dirt Road Queen already has given them reason to celebrate.

“She’s just a professional who does everything right,” Martinez said. “And she seems like she’s getting better and better.”