Thomas is a San Francisco-based Kiwi who also has a Matapiro Rd property in Hawke's Bay called Willow Tree Farm. He and the wife breed showjumping mounts in LA and initially operated from Cambridge.
Designated Driver, who will start from barrier five in a field of seven with Robert Hannam in the saddle, has won the first two races in her five starts with the training couple.
She was 12th in the 1400m JB Organics HB Spring Racing Carnival finale on October 4 but bounced back with a third at the Rydges Wellington Premier a fortnight later.
The sprinter was runner-up to Guy Lowry and Grant Cullen-trained Adventador in the 1200m Levin Stakes on December 6.
"We got beaten by a cigarette paper," she says of the loss by a nose for a horse who can turn it on from a heavy 10 to dead 6 track.
The running joke with Lowry, for whom Thompson-Brown did track work for almost a decade, is that he has a "Hanavarian" (solid showjumper) in Adventador.
Thompson-Brown suspects Designated Driver, sired by Danroad (Aust) from Smashed All Night (NZ), is partial towards running in the capital city.
She describes the horse as "an absolute sweetheart" who eats and travels well.
Her docility should not be misinterpreted for lacking a killer instinct when she's jostling for position on the track.
"Oh she's got an attitude when working and she wants to be in the front."
A question mark hangs over Designated Driver in today's race over 1400m, considering her proven record 200m below that distance. Earning points for The Telegraph is not a given today, either.
"It'll be a monumental stuff up if we finish last because we'll lose points," says Thompson-Brown of a horse that doesn't like a track below dead 2.
The trainer is confident the use of sprinklers at the course for the past week will ensure the track doesn't fall below a dead 4 on a cloudy, 25C day.
She and her husband have equal input in schooling Designated Driver.
"Mike does the quite gallops and slow work and I ride her in fast runs," she explains, adding her "midget" stature allows her to do key rides.
Brown is from England where he used to be an amateur steeplechase jockey.
The couple applied for a training licence about five years ago, not long after an injury to Thompson-Brown, an accomplished showjumper whose family have a rich history in everything equine.
"I gave up showjumping when a ramp [on a float] fell on my head."
Showjumping demands time, too, so they felt she couldn't do justice to both and thoroughbred racing prevailed.
The couple have 10 horses at work and own one of them, Samagon, at their stables.
They also have two terriers, Bella and Kenny, for racing at the Hawke's Bay A and P Show but "it's just for some good fun".
Lowry/Cullen, John Bary and Patrick Campbell are among the Hawke's Bay trainers who have several horses in the eight-race meeting today.
Napier-based jockeys Shannon Doyle and Miranda Dravitzsky are also in the saddle, albeit not always on Bay trainers' mounts.