Amphitrite has capped a meteoric rise with a last-to-first victory in the Group One Thousand Guineas.

The Darren Weir-trained filly's unbeaten spring began just over a month ago with victory in the Sale maiden in country Victoria and she has continued to rise to every challenge in her three starts since.

After a convincing win in the Group Two Edward Manifold Stakes (1600m) at Flemington last Saturday connections made the decision to back-up Amphitrite in Saturday's $500,000 feature for fillies at Caulfield.

With Craig Williams in the saddle, Amphitrite unleashed a powerful finish down the outside of the field to grab Fundamentalist in the final strides of the 1600m race.

Amphitrite ($13) defeated Fundamentalist ($101) by a head with 1-1/4-lengths to Group One winner Seabrook ($26) third.

"It's amazing where these horses come from," Weir said.

"Obviously she showed us a little bit in her first preparation but nothing like this.

"She went out and matured and turned into a nice, big strong filly.

"She has trained well and continued to train well.

"She's a beauty. And the further she goes the better she'll get."

Weir saddled up three runners in the Thousand Guineas with Amphitrite considered the best of the trio in the market.

Stablemates Anjana and Krone ran fourth and eighth respectively.

"She (Amphitrite) was in great shape but I didn't know whether any of my three fillies were good enough," Weir said.

"But they all ran as good as they could run.

"And the wide barriers weren't such a disadvantage as I thought they would be."

Amphitrite could continue her spring preparation in the Wakeful Stakes (2000m) at Flemington next month.

The previously unbeaten Smart Melody was sent out the $2.15 favourite and bounced to the front with second favourite Thrillster on her outside.

The pair gave a kick early in the straight before being collared, with Fundamentalist bursting from the pack inside the final 200m before Amphitrite wound up out wide.

Smart Melody, who jockey James McDonald said was just over-doing it through the middle stages of the race, finished seventh.

Fundamentalist's jockey Luke Nolen said the runner-up ran a terrific race.

"The winner must have run a real good sectional to beat us," he said.