The approval of the unpopular Greek rescue package, pushed by Merkel, further worsen the attitude of the voters toward the states government.
A YouGov poll on Saturday showed that 21 percent of state voters would change their vote due to the Greek bailout.
"This is rare and will play a determining role," said by Klaus- Peter Schoeppner, head of the polling institute Emnid.
The election of NRW is traditionally taken as a weathervane for the national election. This defeat really challenged the Merkel's government, which operated from last October and added more uncertainties in the future.
In 2005, the CDU defeated SPD, which had ruled the state since 1966, before Merkel won the national election later that year.
In 1995, Johannes Rau from SPD formed a state administration with the Greens, while in the federal level, Gerhard Schroeder ( SPD) and Joschka Fischer (Green) beat Helmut Kohl's CDU in election to form a coalition government in 1998.