Picture: Nicole Gibbs in action during the Aegon Challenge in Nottingham. (Copyright free images)
American Nicole Gibbs battled past top seed Misaki Doi, while Britain's last singles hope Katie Boulter also went out of the Aegon Challenge.
Teenage wild card Boulter was beaten by Tunisian qualifier and World No. 167 Ons Jabeur 6-2 6-4 in the second round at the Nottingham Tennis Centre.
In an exhausting three-setter, Gibbs took 2 hours 16 minutes to overcome World No. 98 Doi 7-5 3-6 7-5.
Before arriving in the East Midlands for the Aegon Challenge, Gibbs had never won a professional match on grass.
In fact, the only professional match the World No. 159 had played on the surface before this week ended in a straight sets loss to Austria's Yvonne Meusburger in the first round of Wimbledon qualifying last year.
"I had no idea that I could play tennis on grass to be honest," said Gibbs, who takes on Lesia Tsurenko in Friday's quarter final.
"My gosh we had one of the most physical first sets that I've ever played.
"We were just both crushing the ball, running down a lot of balls, so it was very physical.
"I was down 5-4, 40-0 on my serve and got a few clutch serves in. We then had a pretty epic point at 30-40 of that game that kind of changed the momentum of that set. I got really lucky to get away with the first."
Doi prevailed in an equally enthralling second set, while a break of serve midway through the third put the No. 1 seed in a commanding position.
Gibbs hit back as her Japanese opponent looked to serve out the win and then with her second successive break the American sealed victory.
"She stepped it up and played better at the end of the second set and I reversed it on her at the end of the final set," said Gibbs.
"This tournament is meant to get me ready for Wimbledon, so going deep into the tournament is great preparation for me."
In the men's singles event, fifth seed Sam Groth takes on eighth seed Rajeev Ram in the last four while qualifier Nick Kyrgios faces Miloslav Mecir Jr in the other semi-final.
Groth, who reached the French Open doubles semi-final with Andrey Golubev, finally overcame Gilles Muller, having had his hopes in South Korea and Taiwan ended by the World No. 108.
Second seed Muller beat the Australia twice during an 18-match winning streak which saw him clinch three consecutive ATP Challenger titles in Asia. Muller's remarkable run came to an at the semi-final stage of Aegon Trophy in Nottingham on Sunday.
"He was on a bit of a role in Asia and has been playing well here too, but I knew what I wanted to do out there," said Groth.
"I felt I executed in the right moments and came away with the win."
Muller's doubles hopes with Jamie Delgado were also dashed on Thursday, with the top seeded pairing of Rameez Junaid and Michael Venus moving into the final with a 6-3 6-7(3) 10-8 win.
The Antipodean duo take on Belgium's Ruben Bemelmans and Go Soeda of Japan in Friday's final after they overcame the British team of Edward Corrie and Daniel Smethurst 7-6(3) 7-6(6).
Entry to the Aegon Nottingham Challenge is free for all spectators.
For more information, including orders of play and a full list of results for the Nottingham Festival of Tennis, visit www.nottinghamfestivaloftennis.com.