Top seed Kristina Mladenovic retired from the Ladies Open Lugano on Thursday after being troubled by a back injury in her first-round encounter with Tamara Korpatsch.

The world number 19 from France lost a first-set tie-break 7-5 and was a break down at 3-2 in the second when she brought the contest to a premature end.

Victory for the 176-ranked Korpatsch was the German's first over a top-20 opponent and she will be up against fellow qualifier Kathinka von Deichmann in the second round.

Von Deichmann also advanced without completing her first-round encounter, Laura Siegemund retiring when 3-2 up in the second set after losing the first on a tie-break.

Seeds Anett Kontaveit and Svetlana Kuznetsova were knocked out by Vera Lapko and Mona Barthel respectively.

Kontaveit, seeded four, was beaten 3-6 6-4 6-3 by world number 130 Lapko, while wildcard and fifth seed Kuznetsova went down 4-6 6-3 6-4 to German Barthel.

Aryna Sabalenka was the first player to reach the quarter-finals, seeing off Polona Hercog 6-3 6-1.