Maria Sharapova's winning return grabbed the headlines at the Stuttgart Open on a day when fifth seed Garbine Muguruza missed out on a spot in the last eight.

Wednesday's action marked Sharapova's comeback to the WTA Tour following a 15-month absence after she was found to have taken the banned steroid meldonium.

Opponent Roberta Vinci was one of many to have criticised the decision to hand the five-time grand slam champion a wildcard, but Sharapova marched through to round two with a deserved 7-5 6-3 triumph in Germany.

She was followed on court by Muguruza, who lost all her momentum in a second-set tie-break against world number 73 Anett Kontaveit.

The Spaniard was beaten 2-6 7-6 (7-1) 6-1 in one of only two matches to go the distance.

Kontaveit joined Simona Halep in reaching the quarter-finals, the Romanian fourth seed overcoming Barbora Strycova 6-2 6-3.

Briton Johanna Konta, whose recent Fed Cup outing was overshadowed by the abuse she received from Romania captain Ilie Nastase, shrugged off that unsavoury episode in a 7-6 (7-5) 3-6 6-1 win over Naomi Osaka.

In other first-round matches, Kristina Mladenovic set up a showdown with reigning champion Angelique Kerber after a 6-4 6-2 victory over Mirjana Lucic-Baroni, Carla Suarez Navarro beat Tamara Korpatsch 6-2 6-4, Elena Vesnina downed Daria Kasatkina 7-6 (7-2) 6-2, while Coco Vandeweghe saw off Jelena Ostapenko 7-6 (7-3) 7-6 (7-3).