The Victorian opener dominated day three of the last-round game at the WACA on Monday, top-scoring with 151no.
While the visitors learned early in the day they were effectively out of contention to play South Australia in the final, they are doing their best to frustrate WA's bid.
Victoria had reached 8-335, an overall lead of 346, and Peter Siddle is yet to score.
Kellaway, 22, had faced 310 balls for his highest first-class score, with 17 fours and a six.
Joel Paris glared at the umpire for several seconds late on Sunday when his lbw appeal against Kellaway with the first ball of Victoria's second innings was turned down.
The WA left-armer's frustrations only compounded on Monday as Kellaway scored his second first-class ton.
No.3 Blake Macdonald dominated with 60 out of his partnership of 69 with Kellaway to help set up the Victorian innings.
WA hit back midway through the innings as off-spinner Corey Rocchiccioli took two wickets in an over and Victoria lost 3-1.
But captain Will Sutherland (23) and Fergus O'Neill (26) provided crucial late-order support for Kellaway as Victoria extended their lead past 300.
Victoria were well-set at 2-190 before Paris, who toiled impressively throughout Monday, dismissed Oliver Peake for 21.
In the next over, Rocchiccioli snared Peter Handscomb for one and Harry Dixon for a duck and suddenly WA could sniff a run chase of less than 300 on the last day.
Kellaway combined with the lower order to play spoiler roles through to stumps, with the news from Adelaide during the day that Queensland's batting bonus point had essentially cruelled Victoria's final hopes.
Victoria's only hope of making the final now is if they win and SA somehow beat Queensland. The much more likely outcome on Tuesday at Karen Rolton Oval is extended batting practice for the home team.
Rocchiccioli had taken 3-85, giving him eight wickets for the match, while Paris had claimed 2-63 from 27 overs.
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