WOODSIDE — Frankie Thieriot and Julie Flettner each rode faultless show jumping rounds to win the two divisions of the $15,000 Woodside Preliminary Challenge at the Woodside Horse Trials on May 25-27.

Riding Euphoria, owned by Tory Smith, Thieriot, of Occidental, won the Horse Division with a score of 27.1 penalties. Riding her own Ping Pong, Flettner, of Petaluma, Calif., won the Rider Division with a score of 27.9.

The Fourth Annual Woodside Preliminary Challenge reached its nail-biting climax on Saturday evening, as a cheering crowd of more than 800 people gathered around the Bay Arena of the Horse Park. A sold-out gathering of 350 people enjoyed a full-course dinner and other entertainment in a ringside tent, while the rest cheered from the rail around the ring.

They were treated to top-class competition. Barbara Crabo, of Scottsdale, Ariz., took the early lead in the Horse Division with a score of 25.9 on her home-bred mare, Over Easy, barely topping Thieriot and Euphoria by 0.4 penalties. Thieriot then gave Crabo just a bit of breathing room on Saturday morning by finishing the cross-county course two seconds slow (0.8 penalties).

Meanwhile, the third- through eighth-placed horses all jumped around Derek di Grazia’s cross-country course clean and fast, meaning that they arrived at show jumping with only four penalties (the price of one fallen rail) separating the top five horses.

Erin Kellerhouse, winner of the Woodside Preliminary Challenge in 2011, increased the pressure by jumping faultless rounds on both her horses, Cat Ballou and Bill’s Midnight Magic, to finish fourth and fifth.

Then Matt Brown of Petaluma rode Aida to a perfect round (28.5), just before Thieriot and Euphoria, an 8-year-old Holsteiner mare, did the same.

As a hush fell over the buzzing crowd, Over Easy, 6, just ticked the natural oxer at fence 3 to drop to third (29.9).

“I didn’t think there was any chance Barb would have a rail down!” said Thieriot, 25.

Thieriot had previously competed her own horse, Fric Frac Berence, for 12 years, through the advanced level, and for the last two years she’s been the face in front of the camera for the video event coverage produced by the U.S. Eventing Association.

“The atmosphere was absolutely electric tonight, and the crowd was really into it,” Theriot said. “It’s neat to experience that here, and I think it really helped Euphoria — she was just flying over those jumps.”

The evening’s excitement had a bigger effect on the Rider Division, where just two of the top six finishers jumped faultless rounds. Besides Flettner and Ping Pong, the other belonged to Brynn Littlehale and Coup D’Etat. Their perfect round, along with a fault-free cross-country performance, propelled them from 10th place after dressage to a final second place (33.9).

So when Flettner, 36, entered the ring, she could afford to lower one rail and still win. It was a cushion she didn’t need.

Ping Pong is a 12-year-old Hanoverian mare she purchased in 2009 and rode in competition for the first time at the May Woodside Horse Trials that year, completing beginner novice. Flettner, an optometrist who works in a veterans’ clinic in Santa Rosa, trains with Matt Brown.

“I was definitely nervous tonight, and [Ping Pong} just went on with it,” she said. “She really rose to the occasion. Even when they played the National Anthem, she stood there looking at the flag.”

Last November, Flettner and Ping Pong won the training three-day event at the Galway Downs International Three-Day Event. The Woodside Preliminary Challenge was their fifth start at preliminary level and the first one at which they’d finished cross-country under the optimum time.

“The Preliminary Challenge has been a goal for me to work for. For me, this is my championship,” she said.

For her championship victory, Flettner received $2,500 in prize money, a Devoucoux Saddle, and other prizes donated by Professional’s Choice, APF, Ride One Video and Four Star Equine Therapy.

Littlehale earned $1,875 in prize money, which was paid to 10th place, a total of $7,500 in each of the two divisions.

For winning the Horse Division, Thieriot received $2,500 and a JRD Custom Saddle, plus the prizes from Professional’s Choice, APF, Ride On Video and Four Star Equine Therapy.

Katie Groesbeck, of Canyon Country, rode her own Oz The Tin Man to win the advanced division. Groesbeck, 22, and the Anglo-Arab gelding took the lead in dressage, with the exceptional score of 27.5, and then recorded the only faultless cross-country round to in by 13.9 penalties. Kelly Pugh, on Copycat Cloe, took second.