After scoring 75 in his side's thrilling one-wicket win against Tasmania on February 10, Curtis continued his fine form to help the Western Australians finish their season on a high.
His 91 off 83 deliveries set up WA for a comfortable chase of Victoria's 231-run target at the WACA on Saturday.
But the 26-year-old was cruelly denied a second century in the competition as his extra-cover strike nestled into a diving Matt Short's hands with his side needing just 37 more to win.
Curtis had allies in Cameron Bancroft (70 off 107) as they established a 134-run second-wicket partnership, and opener Sam Fanning, who had pushed the tempo early with a run-a-ball 31.
Bancroft whacked the winning runs in the 40th over as Western Australia finished on 2-233.
In a positive for the visitors, Kellaway fired a match-high 105 from 117 balls to save them from a humiliating low score after they were sent in to bat.
It took a full toss from seamer Matthew Kelly to dismiss the 23-year-old after his shot to long-on found the safe hands of Ashton Turner in the 49th over.
Opener Short was the next highest scorer for the Victorians with 35 off 43 balls as the visitors struggled to build any serious momentum.
WA's Bryce Jackson continued his red-hot bowling form, grabbing 4-40 after collecting four wickets in his previous One-Day Cup outing against Tasmania.
18-year-old Will Malajczuk also snared 2-48, including the key scalp of Peter Handscomb for a duck.
Victoria finished their season at the bottom of the ladder after making the final last campaign, while Western Australia ended in fourth spot.
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