Katarzyna Piter defeated Mona Barthel 6-3 6-3 in the Stockholm 25K round of 16 on hard. The upset overturned the form book — Mona Barthel came in ranked #186, leading the head-to-head 1–0. Katarzyna Piter claimed a first win over Mona Barthel in two meetings, levelling the head-to-head at 1–1.
Piter K. took it in straight sets.
Katarzyna Piter beat Mona Barthel 6-3 6-3. Umpiry, "Katarzyna Piter vs Mona Barthel — Stockholm 25K Round of 16", https://umpiry.com/match/2011-02-07/barthel-vs-piter-stockholm-25k-r16?utm_source=cite (as of 7 February 2011).