Top-seeded and defending champion Maria Sharapova and second-seeded Australian Open runner-up Li Na highlighted Friday's quarterfinal winners at the $795,000 Porsche Tennis Grand Prix.
The former world No. 1 and reigning French Open champ Sharapova snuck past fellow former world No. 1 and former Roland Garros titlist Ana Ivanovic 7-5, 4-6, 6-4 in 2 hours, 16 minutes, while the former French Open winner Li handled fifth-seeded former Wimbledon titlist Petra Kvitova 6-3, 7-5 on a star-studded Day 4 on the red clay at Porsche Arena.
Sharapova is now 6-2 lifetime against Ivanovic, including wins in their last five encounters and a victory in the 2008 Aussie Open final.
The Porsche global brand ambassador Sharapova beat Victoria Azarenka in last year's marquee finale in Stuttgart.
Sharapova's semifinal opponent will be third-seeded German crowd favorite Angelique Kerber, while Li will battle surprising American qualifier Bethanie Mattek-Sands on Saturday.
Friday's other quarterfinals saw the left-handed Kerber top Kazakhstan's Yaroslava Shvedova 6-3, 7-6 (7-2) and Mattek-Sands disappoint the home faithful with a 6-4, 6-2 spanking of oft-injured German Sabine Lisicki.
The 2013 Stuttgart champ will collect $130,000 and a new Porsche 911 Carrera.