A key ally of Chancellor Angela Merkel on Tuesday lost his post as the centre-right party's parliamentary chief in a vote that underlined strong headwinds faced by Germany's veteran leader.
Volker Kauder, who has headed the parliamentary group of Merkel's CDU and Bavarian allies CSU for 13 years, lost in a re-election battle to challenger Ralph Brinkhaus, a relative unknown.
The shock 112-125 result came a day after Merkel was forced to admit mistakes in her handling of a row surrounding Germany's outgoing domestic spy chief.
Observers and opponents called the vote a slap in the face for the chancellor, who had campaigned hard for Kauder's re-election.
"This is a revolt against Merkel," wrote the centre-left SPD's parliamentary group leader Thomas Oppermann on Twitter minutes after the result was published.
Deputy leader of the SPD, Ralf Stegner noted that the result "shows how deep the erosion of power within the (CDU-CSU) is".
Earlier Tuesday, Spiegel Online had said that a win by Brinkhaus would mean that "Merkel should really clean out her office in the chancellery immediately -- his election would be nothing short of a vote of distrust against the leader of the government."
In a brief statement, Merkel thanked Kauder and congratulated Brinkhaus, adding that "this is an hour of democracy, in which there are also defeats and there's nothing to gloss over."
Brinkhaus himself said opposing Merkel was not his intention of joining the race.
But he felt the parliamentary group needed a change at the top after 13 years.
"It's not about shifting the group in a specific direction, but about an internal positioning of the group and how we can get new momentum," Brinkhaus said ahead of the vote results.
Far-right party AfD gleefully welcomed Kauder's toppling.
"It's over for Merkel: Kauder voted out! Volker Kauder's loss in the election as parliamentary group leader now clearly shows Merkel's loss in power. The twilight of Merkel has finally set in," wrote AfD leader Alice Weidel on Twitter.
After nearly 13 years in power, Merkel has seen support for her centre-right party chipped away by the far right, which has mobilised backing with its anti-immigration stance.
Merkel fateful decision in 2015 to not close the border to hundreds of thousands of asylum seekers at the height of Europe's migrant crisis has proved one of the most divisive policies in her four terms as leader.
