The outdoor hard court tournament in Lexington, Kentucky, marks the first WTA event in the United States since the coronavirus outbreak forced a hiatus.
World number 49 Brady - the highest ranked player in the final four - used a powerful serve to her advantage over Gauff at the fanless tournament, firing off eight aces and winning nearly 85% of her first-serve points, to set up a final clash with Switzerland's Jil Teichmann.
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"I've been working a little bit on all aspects of the serve, mainly the stroke and the timing of the serve, more technique, things like that," said Brady. "If I'm able to serve well, I'm able to start the point aggressive, start it in my favour."
Brady, aged 25, had lost her three other WTA singles semi-finals, but reversed the trend in this clash which lasted just over an hour.
Gauff managed to convert only one break point chance but was not too disappointed afterwards.
"Jenny just played a great match, and I can take away a lot from this week in general. I couldn't have asked for a better week back," she told the media.

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Teichmann, who won both of her two WTA titles at clay court tournaments last year, defeated American Shelby Rogers 6-3, 6-2 to earn her final berth.
"Obviously everyone thinks I'm just a clay court player - I think I've proven it's not only this way," the 23-year-old said. "I've been feeling great on hard courts since the beginning of the year... My goal was just to keep on this level."
Additional reporting by Reuters.
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