World No.49 Boulter fought back to overcome sixth-seeded Ukrainian Marta Kostyuk 5-7 6-2 6-2 in the San Diego Open final on Sunday.
She became the lowest-ranked player to win a WTA 500 title since 2021 and is set to soar to a career-high No.27 in the world when the updated rankings come out.
Her victory came after world No.9 de Minaur had downed Casper Ruud on Saturday night to claim the Mexican Open title in Acapulco for a second straight year.
After his victory, de Minaur revealed he was planning to forgo the post-tournament party and make a travel dash to be courtside to watch Boulter's final.
In her on-court victory speech, Boulter thanked a smiling de Minaur for his support.
"I want to say a small special thank you to my boyfriend," she said.
"He finished last night at midnight. And I really want to embarrass him, so he got a 4.15 taxi and a six o'clock flight to be here today, so I do appreciate it."
Boulter's only previous WTA title came in the lower-tier WTA 250 Nottingham tournament on grass last year.
All five of Boulter's victories at the San Diego Open were over top-50 players.
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