Ana Konjuh upset 2nd seed Yulia Putintseva at the Serbia Ladies Open in Belgrade on Wednesday, while Nadia Podoroska and Rebecca Peterson, seeded 5 and 7 respectively, also reached the quarter-finals.
Konjuh started her week in the qualifying, beating both Jule Niemeier and Viktoriya Tomova from a set down to reach the main draw where she edged out Alison Van Uytvanck before taking out Putintseva, who was the favourite for the title, 6-3 6-4.
The Croatian takes on Podoroska for a place in the semi-finals after the Argentine took out Oceane Dodin from France on Tuesday.
Podoroska was not at her best in the early weeks of the season, but since returning to the European clay the Argentine is finding some form.
In Rome, she beat Serena Williams in straight sets in the second round only to fall short in the third against Petra Martic, but she has looked sharp once again so far in Belgrade.
Peterson, who is from Sweden, dropped the first set to Ajla Tomljanovic but levelled by claiming the second before a left hip injury has forced the Australian out of the WTA 250 tournament after an hour and 46 minutes on court and just 3 games played in the decider.
The 28-year-old Aussie had started strongly against the 7th seed but after the Swede bounced back to level the match at set all Tomljanovic was unable to continue and Peterson advanced, 4-6 6-2 2-1 retired.
Peterson, after a miserable campaign in 2020, has found a measure of form so far in 2021, with 6 wins to her name from 11 matches played coming in to Belgrade, and she has since added victories over Nina Stojanovic, from a set down, and now Ajla Tomljanovic, but faces a tough test against Paula Badosa, the No 4 seed.
The Spaniard has been in excellent form of late, enjoying a career-best result at the Madrid Open, where she reached the semi-finals and picked up wins over Anastasija Sevastova and 8th seed Belinda Bencic, amongst others.
She has backed that up with assured straight-sets wins over Andrea Petkovic and Mihaela Buzarnescu.
Meanwhile, Aliaksandra Sasnovich from Belarus secured her second win of the week to reach the quarters after two-and-a-half hours seeing off Spain’s Cristina Bucsa, 6-4 5-7 6-0.
Ranked 103, Sasnovich, who romped away with the deciding set over the World No 172, takes on Maria Serrano after the 115th ranked Colombian battled past Russia’s Kamilla Rakhimova, 4-6 6-3 6-4.
Two second round matches remain outstanding.
Canadian Leylah Fernandez is waiting to play lucky loser Viktoriya Tomova of Slovakia, who replaced top-seed, the 30th ranked Anastasia Pavlyuchenkova after the Russian pulled out of the event with an abdominal injury; while Anna Kalinskaya, who caused the sole upset by seeing off 6th seed Kristina Mladenovic in straight sets on Tuesday, was a set all against Hungarian qualifier, Reka-Luca Jani, when play was suspended on Wednesday.