Top seed Sabine Lisicki was forced out of the Auckland Classic on Thursday when she suffered an abdominal injury during her quarter-final against fellow German Angelique Kerber.
Lisicki, who has struggled with her timing in a series of mixed performances throughout the week, sought treatment for the injury after she lost the first set 6-4 and continued to have treatment between games.
She lasted until the eighth game of the second set, when she was trailling 4-3 and decided she could not carry on.
The world number 15 also had issues with cramping in her calf during her second round victory over Mona Barthel on Wednesday and had already withdrawn from the doubles.
Kerber will meet fourth seed Flavia Pennetta in the semi-finals after the Italian effortlessly accounted for Russia's Elena Vesnina in the first match on Thursday, romping to a 6-2 6-1 victory in 68 minutes.
The 29-year-old Pennetta never appeared ruffled in the match, making few errors and putting the Russian under constant pressure, clinching victory when her backhand return of serve down the line left Vesnina flatfooted.
"I think today was perfect, I didn't make a lot of mistakes, my serve was working good and I'm really proud of the match," Pennetta said. "It was a tough matchup, she is a very good player but I played really good."
China's Zheng Jie also advanced to the final four, where she will meet the winner of the night match between the two-times major champion Svetlana Kuznetsova and Sara Errani.
Zheng also seemed to waste little effort in overcoming Lucie Hradecka 6-2 6-3 in an hour.
"I think the match was amazing for me because it's a new year and this is the first tournament and I'm in the semi-finals, I'm very happy," Zheng said.
"I have played Lucie a few times before and I knew she played aggressively, so I wanted to move her around a lot and it was a good (performance)."