The Hawkesbury-trained galloper won the feature event to make it two country cup wins in her 34-race career.

The Gold Cup win goes alongside the Cowra Cup the mare won in 2014, and that victory was At Twilight's most recent until Sunday.

The Tara and Phillipe Vigouroux-trained six-year-old, starting at the attractive odds of $31, upstaged many of her fancied rivals and jockey Claire Nutman was able to hold off the Kathryn Cahill-trained Two Penny Blue and win by one-and-three-quarter lengths.

"Really delighted, we just adore this little mare," Tara Vigouroux said from the pair's stable at Hawkesbury after the win.

"This is the second country cup for her and she's just tiny, she's be lucky to be 15 hands so that's really little and I'm just thrilled to see her win."

All the pre-race attention was on trainer Mark Milton and his gelding Sooner Or Later and with champion jockey Greg Ryan onboard they started as $2.30 favourites.

But Sooner Or Later again began slowly while Iwilldoit ($18) and Topmast ($8.50) led the field and set an impressive early pace.

The duo got out to a lead of five lengths but by the time the field reached the top of the bend it was anyone's race.

Apprentice jockey Nutman found herself in prime position in the middle of the track and she pushed forward while Mathew Cahill onboard Two Penny Blue ($26) also made a move.

At Twilight, carrying just 52.5kg with Nutman's allowance and coming into the race off a fifth placed finish in this month's Forbes Cup, had the pace to push forward and claim a hugely impressive win.

"Clare is amazing, she rides trackwork for us nearly every morning and rides so many for us on raceday," Vigouroux said of her winning jockey.

"We've got 100 per cent confidence in her and she's an integral part of the team."

The Brian Young-trained Laugharne ($26) held on for third while Blood Red Moon ($5.50) stormed down the outside to finish fourth.

While overjoyed with the win, Vigouroux admitted it brought with it a number of challenges as more weight will now be put on At Twilight's small physique.

"She's so small and when she won at Cowra her benchmark went up significantly and she just had too much weight and it took a while to get back down to where she's comfortable," she said.

"She can't carry that sort of weight in the races over a mile but we're about to have to do the same because her benchmark will spike now so it will be harder to find her races."

Cahill may have missed out on another Narromine Cup but he was the only jockey to record a double on the day with wins onboard Malverna and Northern Act in the first two races of the day.