The eighth seed was 5-2 down in the final set but broke back twice before taking command of the tie-break in a 6-2 2-6 7-6 (7-3) triumph.

Having been dominated in the first set, sixth seed Tomljanovic returned the favour in kind in the second and recovered from an early break in the decider to win five straight games.

But Tomljanovic's nerve failed her when it mattered most as she twice surrendered serve to Yastremska.

The Australian was unable to muster a response when the match headed to a breaker and she now slips to 0-4 in WTA Tour finals.

Teenager Yastremska, meanwhile, continues to see her star rise with a second title now added to the Ukrainian's collection having prevailed in Hong Kong four months ago.