Opposition parties delivered a strong performance in the Czech Republic's Senate elections on Saturday, winning the majority of the 27 seats up for grabs in the 81-seat upper house. The center-right Mayors and Independents party, known as STAN, emerged as the top performer with 10 seats won out of 14 contested, including two secured in the first round.

The Civic Democrats, or ODS, gained seven seats while defending five. Other opposition and center-right groups including the Christian Democrats and TOP 09 retained their seats. The pro-European opposition maintained its overall majority in the Senate.

Prime Minister Andrej Babis's ANO movement, which leads a eurosceptic coalition government, failed to win any of the 13 runoff contests it entered and lost its single existing seat. Babis described the outcome as catastrophic.

Turnout in the second round reached about 21 percent, the highest since 2010. The results followed municipal elections the prior weekend in which ANO won six of the country's 13 regional capitals.

Notable winners included former army chief of staff Karel Rehka and historian Jiri Padevet for STAN, as well as Zuzana Ceralova Petrofova for ODS. The Senate can delay legislation and block constitutional amendments but the outcome is not expected to destabilize the government.

The elections tested the ruling coalition one year after it took power. Opposition leaders celebrated the results as a clear rejection of the government's performance.