LUGANO, Switzerland - Germany's Antonia Lottner scored one of the biggest victories of her career on Tuesday at the Samsung Open presented by cornèr, upsetting top seed and World No.20 Belinda Bencic, 7-5, 6-2.

The two good friends were peers on the junior circuit, but arrived on-court with over 150 places in the rankings between them.

Nonetheless, Lottner managed to break Bencic's serve five times in the second career meeting between the two, to score a Top 20 victory on the season.

The German hammered 27 winners over the course of one hour and 27 minutes, to just 22 unforced errors, and converted on five of the eight break points she held in the match.

The World No.182 won eight of the last 10 games to score the second upset of the day in the Swiss Alps, after Polona Hercog downed No.2 seed Carla Suárez Navarro earlier in the day from a set down.

Despite having never been ranked inside the Top 100, Lottner improved to 3-1 against Top 20 players in her young career.

The 22-year-old twice scored a notable win in back-to-back seasons on the grass courts of the Ricoh Open in 's-Hertogenbosch, upsetting Elise Mertens there last year and Dominika Cibulkova in the year prior.

No.3 seed Viktoria Kuzmova was the highest-seeded winner to score a victory on Tuesday as a result, downing Italian qualifier Giulia Gatto-Monticone, 6-2, 6-2.

Despite seeing the Swiss No.1 upset, the home fans did have something to cheer about on Tuesday as both Timea Bacsinszky and Stefanie Voegele progressed to the second round.

Former Top 10 player Bacsinszky lost just two games in defeating Tamara Korpatsch, 6-0, 6-2, while Voegele downed No.5 seed Pauline Parmentier, 6-2, 6-4.