Labour made the first council by-election gain of 2012, taking a seat at closely balanced St Albans City Council on a big swing.
Candidate Roma Mills won from Liberal Democrats at Batchwood where her party also returned another ward councillor last May.
It is third time lucky in two years for Ms Mills.
She lost by one vote in the ward in May 2010 on the same day as she was also defeated standing for the St Albans parliamentary constituency in the General Election.
The result leaves Tories one seat short of a majority on the city council.
There was one, small, consolation for Lib Dems who, despite a drop in their vote share, took back second place from Conservatives compared with last May.
Counting takes place today at Newcomen, Redcar and Cleveland Borough with a result expected later.
Redcar and Cleveland Borough - Newcomen: Counting today. (May 2011 - Two seats Lib Dem 781, 733, Lab 442, 393, C 100).
St Albans City - Batchwood: Lab 1002, Lib Dem 395, C 347, Green 76. (May 2011 - Lab 1128, C 743, Lib Dem 675, Ind 168, Green 47). Lab gain from Lib Dem. Swing 8.4% Lib Dem to Lab.