Angelique Kerber fell to a shock defeat against Kristina Mladenovic to open up a seedless path to the Stuttgart Open final for Maria Sharapova.

Sharapova booked a quarter-final spot on Thursday with a straight-sets demolition of fellow Russian Ekaterina Makarova, who had beaten seventh seed Agnieszka Radwanska in the previous round.

Anett Kontaveit beat Garbine Muguruza, seeded fifth, to set up a meeting with Sharapova in the last eight and the three-time champion of this event's fortune was capped by potential semi-final opponent Kerber going down 6-2 7-5 to Mladenovic.

Kerber had won here in each of the past two years and was given a warm welcome onto the court in her homeland, but things swiftly went downhill as Mladenovic broke at the first attempt.

Both players comfortably held, until Mladenovic was presented with her first set point, taking it with a whipping backhand return.

The Frenchwoman took momentum into the second set, racing into a 3-0 lead, which silenced the Porsche Arena, although the crowd was stirred as Kerber broke back before saving two break points at 3-4 down.

But there was nothing Kerber could do as Mladenovic opened up two match points at 6-5 up, and converted with a crushing backhand to secure her fourth top-20 win of 2017.

Carla Suarez Navarro is next up for Mladenovic after a 6-2 6-4 win over Elina Vesnina.

Earlier, Sharapova had looked in fine fettle in seeing off Makarova 7-5 6-1.

After 10 games of dominance on serve, Sharapova suddenly clicked up a gear and won eight of the next nine games to race to victory.

The bottom half of the draw also saw shocks as Johanna Konta (6) and Svetlana Kuznetsova were eliminated by Anastasija Sevastova and Laura Siegemund respectively. 

But second seed Karolina Pliskova remains in the hunt and will hope to go even better than her recent semi-final runs in Indian Wells and Miami.

The world number three eased into the last eight here, seeing off Coco Vandweghe 7-6 (7-2) 6-4.

The second seed of the Istanbul Cup had no such luck on Tuesday, however, as Timea Babos was eliminated by defending champion, and doubles partner, Cagla Buyukakcay.

Before this week, Buyukakcay had not won a main draw match on tour since last year's US Open, but home comforts helped her to a 6-4 7-6 (7-5) triumph.

Top seed Elina Svitolina beat qualifier Alexandra Cadantu 6-3 6-3 to seal a quarter-final with Sorana Cirstea. Jana Cepelova, Elise Mertens and Basak Eraydin also secured quarter-final spots on Thursday.