The Christian Democratic Union, led by German Chancellor Angela Merkel, has won an upset victory over the opposition Social Democratic Party in regional elections in the country's most populous state, in a key victory ahead of September's federal elections, the Financial Times reported May 15.

The CDU won 33% of the vote in North Rhine-Westphalia, which is also home to former European Parliament President Martin Schulz, now leader of the SDP, which saw its vote decline to 31% from 39% in 2012, preliminary results showed.

The SPD has ruled the state for all but five years since the 1960s, but this was the third consecutive state test to end in defeat for the party, which also lost earlier contests in Saarland and Schleswig-Holstein.

The CDU could now govern by forming a coalition with the SPD, or else join with the liberal Free Democrats, who only took 12.6% of the vote. The right-wing populist Alternative for Germany gained 7.4%, whereas the far-left Green Party secured 6.4%.