Former Victorian galloper Portrait Lass scored an upset win in today's feature event at Northam: the $22,500 Matriarch Cup.

The Perugino mare, courtesy of a perfect ride by Jessica Valas, scored in a thrilling contest to defeat Agribiz and New Faith with the highly-rated Jacita back in fourth place.

Trainer Grant Williams has certainly found the winning touch with Portrait Lass and her record since arriving in Western Australia stands at two wins and a second placing from five starts.

Key Business mare Agribiz continues her consistent form and it was only a bob of the head that denied her victory.

The highly regarded Jacita, from the Danny Morton stable and race favourite, just failed to run on and was placed fourth.