Story highlights Win comes in home state of Merkel's opponent in upcoming national vote

Election is third recent victory for Merkel's party

(CNN) German Chancellor Angela Merkel's Christian Democratic Union scored a major victory in elections in the German state of North Rhine-Westphalia on Sunday.

Preliminary results showed Merkel's CDU receiving 33% of the vote in North Rhine-Westphalia, or NRW, followed by the Social Democratic Party's 31.4%.

It's a major upset for the SDP, in a state it has governed almost without interruption since 1966. NRW is Germany's most populous state and the home of SPD national leader Martin Schulz, the former EU Parliament president who will face Merkel in federal elections later this year.

CDU General Secretary Peter Tauber crowed over the election results at a party gathering in Berlin, saying his party had "conquered the heart" of the SPD.

Schulz called the loss on his home turf "a truly crushing defeat."

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