But the monumental win was not appreciated by all, with Kyrgios - who also happens to be Tomljanovic's girlfriend - rubbishing the victory as "trash".
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.
Tomljanovic expressed her frustration to the umpire and asked whether her opponent had specified her injury. "I had to hit winners as she was consistent at the baseline".
Tomljanovic: "Every player is supposed to ask a player..."
Yastremska was down 5-2 in the third but twice the Australian Tomljanovic failed to close it out.
On the court at the Australian Open in January Kyrgios told interviewers: 'It's when I'm with her that I am the happiest'.
And that's how it ended.
Instead, she briefly clasped her opposition's hand near her own chair and quickly packing up her gear before grimacing next to Yastremska on the podium. The teenager then came through in a decisive tie-break to seal the victory.
There were quite a few on Twitter who agreed with Kyrgios' assessment on Yastremska's gamesmanship but others pointed out the need to be tough enough to handle such situations which might have well been within the laws of the game.
"Thanks to my coach for always believing in me".
It was Yastremska's second career title while Tomljanovic has now fallen to 0-4 in WTA singles finals, losing three in the past year after defeats in Morocco and South Korea.