Defending champion Jelena Ostapenko booked her place in the last 16 of the Luxembourg Open with a comfortable straight-sets win over Jule Niemeier.

The world number 30 came out on top 6-2 6-2 in a little under an hour to set up a meeting with Arianne Hartono, who earlier beat Anna-Lena Friedsam 7-6 (7-5) 3-6 7-6 (7-4).

Fifth seed Marketa Vondrousova also shuffled through to the next round thanks to a 6-2 6-3 triumph against Alison Van Uytvanck, while Zarina Diyas will face tournament favourite and Olympic champion Belinda Bencic next after beating Anna Karolina Schmiedlova in three sets.

Aliaksandra Sasnovich was made to work harder for her 7-5 7-6 (8-6) win against Lesia Tsurenko, with that the longest straight-sets match of 2021 so far at two hours and 30 minutes, according to the WTA.

Greet Minnen and Mandy Minella were also victorious on Tuesday, overcoming Nuria Parrizas-Diaz and Varvara Gracheva respectively.

At Zavarovalnica Sava Portoroz in Slovenia, meanwhile, home favourite Kaja Juvan eliminated top seed Petra Martic with a 6-3 6-4 win. Sweden's Rebecca Peterson was another seed to fall, going down in straight sets to Lucia Bronzetti.