Unseeded Austrian Tamira Paszek advanced to her first WTA Tour semi-final since 2012 after outlasting Kirsten Flipkens in three sets at the ASB Classic in Auckland on Thursday.
Paszek's career had been at the crossroads prior to the tournament in New Zealand, after being hampered by form and injuries.
But the 25-year-old reached her first premier semi-final since defeating Marion Bartoli at the Aegon International three-and-a-half years ago thanks to a 6-4 6-7 (3-7) 6-3 win over Flipkens.
Paszek, who upstaged Francesca Schiavone and fourth seed Svetlana Kuznetsova to reach the quarters, needed seven match points to see off her Belgian opponent in a match lasting almost three hours.
"I'm delighted that I was strong enough mentally to focus and deal with the setbacks and actually close out the match," Paszek said.
"In the second set I felt like someone pulled the plug and I had no energy left.
"It was kind of weird, I felt a bit sick on court, and it was tough because she was pushing a lot and playing more aggressively than earlier in the match.
"In the end there were some nerves out there, but respect to her [Flipkens], she kept fighting until the end."
Standing in the way of Paszek and a spot in the final is Julia Goerges, who outlasted Nao Hibino 6-7 (3-7) 6-2 6-4.
Fifth seed Sloane Stephens also won through to the last four via a 7-6 (8-6) 6-3 victory against Naomi Broady.
Stephens will face third seed Caroline Wozniacki on Friday after the Dane demolished Alexandra Dulgheru 6-1 6-0 in Thursday's final match.