The 19-year-old Keys was totally dominant against her 24-year-old compatriot, hammering 38 winners in the win.
Keys made the perfect start as she broke Brengle's serve in the opening game.
Brengle's struggled with her first serve and was fortunate to be broken just twice in the opening set.
Keys has the ability to find the right angle for winners, and did so converting a break point at the fifth attempt in the third game of the second set.
Brengle responded swiftly to immediately break back and started to play some of her best tennis to keep the match alive.
In the ninth game Keys broke again, and held her nerve to clinch the victory with a third match point a few moments later.
She will now meet either Venus Williams or sixth seed Agnieszka Radwanska in the last eight.