Serena Williams knocked out in Lexington

The number one seed won the first set but her young countrywoman fought back and forced a decider which went to an enthralling tie-break.

And the Charleston native secured her place in the semi-final with a 1-6, 6-4, 7-6(4) triumph.

Serena had beaten older sister Venus in another three-set clash on Thursday - and her first-round match against another American, Bernarda Pera, had also gone the distance.

Rogers will now face Switzerland's Jil Teichmann, who beat Cici Bellis 6-2, 6-4.

Earlier in the day, Jennifer Brady defeated the conqueror of Johanna Konta, Marie Bouzkova, 6-1, 6-2.

Coco Gauff, the 16-year-old sensation, plays Ons Jabeur in the day's final match.