Labour took one of the Dogsthorpe seats from the Liberal Party in the first result of the night.
Dennis Jones stormed to victory in the seat vacated by former Mayor of Peterborough Keith Sharp.
The Liberal Party now hold two of the three seats in the ward.
Mr Jones, a lifelong Labour supporter who joined the party locally in 2015, said: "To tip the balance in Dogsthorpe by so much is humbling.
"I'm the first Labour councillor in Dogsthorpe for 38 years so to win by almost 400 votes is good. I didn't expect to win by so much.
"Labour are popular at the moment and we ran a good campaign and I hope to be a good candidate."
Dennis Peter JONES (Labour and Co-operative) 954
Sandra RINGLER (Liberal Party) 560
Christopher Michael MOON (Conservative) 255
Romina CAMMARATA (UKIP) 88
Carolyn ENGLISH (Green) 58