MONTREAL - The Parti Quebecois opposition easily held on to a Montreal-area provincial riding in a byelection on Monday.

PQ candidate Martine Ouellet, an engineer at Hydro-Quebec, defeated the governing Liberals' Simon-Pierre Diamond and five other hopefuls in the riding of Vachon.

With more than half of the 172 polls reporting, the Pequiste held a lead in the popular vote by 59 per cent to 24 per cent over the Liberal.

Premier Jean Charest called the byelection after the PQ's Camil Bouchard resigned from politics earlier this year.

The PQ has held the riding since 1994.

In the 2008 general election, Bouchard won Vachon with 48.7 per cent of the vote and a majority of 4,477 votes over his Liberal opponent who had 32.3 per cent. The ADQ candidate had 13.7 per cent.

Diamond was an ADQ member of the legislature in another riding between 2007 and 2008. His victory at the age of 22 in 2007 made him the youngest person ever elected to the national assembly.

Monday's result leaves the governing Liberals with 66 seats in the 125-member national assembly. The PQ has 51, the Action democratique du Quebec four, and Quebec solidaire one. There are also three Independents.

Turnout at 10:30 p.m. was pegged at 29 per cent.