Stuttgart, Germany (SportsNetwork.com) - Second-seeded Simona Halep and former world No. 1 Caroline Wozniacki secured berths in Saturday's semifinals at the Porsche Tennis Grand Prix.

The Romanian star Halep, who will replace Russian Maria Sharapova as the new world No. 2 on Monday, got past Italian fellow French Open runner-up Sara Errani 6-4, 6-4 on the indoor clay at Porsche Arena.

The hot Halep has won 16 of her last 17 matches, including recent titles in Dubai and Indian Wells.

Last year's Roland Garros finalist's semifinal opponent will be the Danish Wozniacki, who blitzed eighth-seeded Spaniard Carla Suarez Navarro 6-0, 6-3 on Day 5. Wozniacki was a Stuttgart runner-up four years ago.

Halep is 2-1 against last year's U.S. Open runner-up Wozniacki, including a semifinal victory in Dubai in February.

The 23-year-old Halep shrugged off death threats from a stalker to take her place in the final four here.

She received a death threat from a Danish fan via Twitter on Thursday and Stuttgart tournament organizers have stepped up security around her.

"I can't comment on it. I am here to play tennis. Other people will take care of it," said Halep.

The obsessed fan is believed to have bombarded Halep with a series of messages via social media.

Meanwhile, unseeded German crowd favorite Angelique Kerber upset sixth-seeded Russian fellow left-hander Ekaterina Makarova 6-3, 6-2 to reach the semis.

Kerber's semifinal opponent will be surprising American Madison Brengle, who overcame France's Caroline Garcia 3-6, 6-3, 6-3.

The 25-year-old Brengle is a Delaware native who reached her first-ever WTA final in Hobart, Australia, back in January.

The 2015 Stuttgart champ will earn $108,000 and a new Porsche 911 Carrera sports car.