Qualifier Danielle Collins overpowered her childhood idol Venus Williams 6-2 6-3 in a stunning quarter-final upset at the Miami Open Wednesday.
Collins, belying her 93rd ranking, pounded winner after winner to beat fellow American Williams at her own game and set up a semi-final against French Open champion Jelena Ostapenko.
Latvian Ostapenko overpowered Ukrainian fourth seed Elina Svitolina in two tiebreaks to win 7-6 (3) 7-6 (5) in an afternoon match to reach the Miami semis for the first time.
Thursday's other semi will pit American 13th seed Sloane Stephens against unseeded Victoria Azarenka of Belarus.
Collins played with manic intensity against eighth seed Williams, repeatedly going for broke with groundstrokes that painted the lines and ran her opponent ragged around the Crandon Park centre court.
The 24-year-old is finally finding her feet at the highest level, as she showed by keeping the pressure on Williams with victory in sight.
Earlier, sixth seed Ostapenko was far from her best in her quarter-final, spraying the court with 44 unforced errors and having her serve broken six times on a windy day.
Yet the 20-year-old's aggressive approach, stepping into the court to take Svitolina's second serves early and targeting the lines with her powerful backhand, paid off in the match's biggest moments.
After Svitolina saved three consecutive match points in the second set tiebreak, Ostapenko hammered her 41st winner, a crosscourt backhand, on match point to end the nearly two hour contest.
Ostapenko said she followed coach David Taylor's advice to stay on the attack against the defensive-minded Svitolina even when she was having trouble with her accuracy.
Ostapenko has now won both of her meetings against Svitolina, included a victory over the 23-year-old at Wimbledon last year.