Unseeded American Sloane Stephens became the first US Open women's semi-finalist by beating Latvia's Anastasija Sevastova in a final-set tie-break.
The 24-year-old, ranked 83rd as she makes her way back from injury, won 6-3 3-6 7-6 (7-4) in New York.
Sevastova beat Maria Sharapova in the previous round but Stephens played superbly to twice come back from a break down in the final set.
She will play compatriot Venus Williams or Petra Kvitova in the last four.
More to follow.