Chasing her first career crown, sixth-seeded Tomljanovic found herself up against it as 18-year-old Yastremska came out of the blocks quickly, wrapping up the first set in 33 minutes.
"The match was really tough for me", Yastremska said.
"No, she didn't tell me", the umpire said.
Upon winning the deciding tiebreak, Yastremska fell to the court and began sobbing on her back, reminiscent of the tears she shed after being crushed by Serena at the Australian Open 2019 round of 32 last month. The teenager won the opener 6-2, but then she lost the second set with the same scoreline.
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The Australian's anger derailed her course to victory as Yastremka completed a major turnaround to win the match 6-2 2-6 7-6 (7-3) as Tomljanovic dropped four straight games.
Then in the tie-break, Yastremska took full charge with some deep groundstrokes, eventually blasting a forehand victor on her first match point to wrap up the victory.
It was a familiar heartbreak for Tomljanovic, who has failed to win a WTA event despite reaching the final four times in her career.
Tomljanovic looked shattered by the result and gave her opponent a quick handshake near her chair rather than meeting her at the net. "She is in pain and were watching me on TV", added Yastremska who will rise to No 43 in the world.
"This is one of the nicest tournaments I've been to so far".
The 18-year-old is experiencing an wonderful ascent in her young career during the last few months.