The 18-year-old swatted aside the tournament's No.5 seed 6-1 6-2 on Wednesday to register her biggest win of her career.
Joint, the world No.103, was set to rise to No.87 after her impressive 6-3 6-2 win over Julia Grabher in the opening round, but her latest conquest will see her soar even higher in the standings.
The rising star of Australian tennis set herself the goal of cracking the top 100 in 2025, but has accomplished that just two months into the year.
Joint will now meet Elina Avanesyan for a place in the last four after the Armenian defeated Spaniard Jessica Bouzas Maneiro 6-1 6-4.
Joining them in the quarter-finals will be Daria Saville, the Australian overcoming Anhelina Kalinina 4-6 6-2 6-2.
The 30-year-old will now play No.2 seed Paula Badosa, who crushed Jaqueline Cristian 6-2 6-1.
In Austin, Ajla Tomjlanovic displayed her never-say-die attitude to down Jodie Burrage and reach the quarter-finals of the ATX Open.
The Australian fought back from a set down before prevailing 6-4 6-3 6-0 to eliminate Burrage, who had put paid to Petra Kvitova's comeback in the opening round.
Burrage enjoyed 10 break-point opportunities against Tomjlanovic, who rallied hard to concede just one of those chances.
The victory takes the injury-prone Tomjlanovic a step closer to achieving her goal of qualifying on her own steam for the French Open - the second grand slam of the year - at Roland Garros starting on May 25.
Like in the previous round when Kvitova had to endure 14 aces from Burrage, world No.111 Tomjlanovic faced a similar barrage with the Brit delivering 11 more.
But the 31-year-old Tomjlanovic, who once rose to No.32 in the world before injuries curtailed her progress, held firm to book her place in the next round against Ena Shibahara.
Japanese star Shibahara was made to fight right to the end by Kim Birrell, before emerging 6-3 4-6 6-4.
The Australian went toe to toe and remained in the contest throughout despite her serving wobbles - she double faulted eight times - and Shibahara's 11 aces.
Jessica Pegula is the top seed in the tournament and the American will now meet Anna Blinkova in the quarter-finals.
Both Pegula and Blinkova enjoyed convincing straight-sets victories over Spaniard Nuria Parrizas Diaz (6-1 6-3) and German Tatjana Maria (6-2 6-2) in the quarter-finals respectively.
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