A "free for all" at the polls saw Labour lose 10 seats, while breakthroughs by the Greens and UKIP saw both parties enter the chamber for the first time.
the ruling group had a firm grip of Sunderland City Council, holding 60 out of a total 75 seats.
But by the end of the night the red rosette crowd was down by 10, following a slew of gains by their political opponents.
The Liberal Democrats managed a double win in Sandhill, which was electing two councillors following the resignation of Lynn Appleby earlier in March, less than a year after she was first elected.
But Niall Hodson was left ruing what he saw as a golden opportunity to steal even more seats from Labour.
"It's been an extremely bad night for the Labour Party, it's been an absolute free for all," he said.
"I've never seen results like this in Sunderland, previously it's been Labour, Lib Dem and Conservatives, but it's now represented by basically every UK political party."
It was almost as good a night for every other main party as it was a bad one for Labour.
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The Greens gained their first ever council seat in the North East, toppling Labour in Washington South - the former ward of disgraced councillor Paul Middleton, who was forced to quit the city council following his conviction for a child sex offence earlier this year.
UKIP were another party which used the night to make its debut in the city council chamber, with three seats.
And the Conservatives were also successful, gaining an extra four seats.
The night's results still leaves Labour in overall control of the city, but council leader Graeme Miller conceded it had been a "terrible night for Sunderland Labour".
He said: "My gut is national issues around Brexit caused a lot of Labour voters to not vote for us or for other parties.
"They're not happy as a city which voted to leave that we haven't allowed that to happen and they see us as wanting to stay."
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