St Mirren left Glasgow with all three points following a thoroughly deserved and in the end comfortable victory.
There was little between the sides during the early exchanges, with Thistle's first chance falling after 19 minutes when Jamie Mitchell should have done better with a near post shot. St Mirren's first chance arrived courtesy of Thistle keeper Kenny Arthur, who dropped an innocuous cross but the danger was cleared.
The half ended with Thistle having their best chance when Billy Gibson and Juan Ramon Escalas linked well on the edge of the box and Gibson's shot was deflected on to the post before being cleared for a corner.
We hoped for better in the second half and St Mirren duly obliged by taking the game to Partick, and after 51 minutes they got their reward when Kirk Broadfoot was upended in the box. Brian McGinty took the penalty and fired the ball low past a despairing Arthur.
St Mirren were now in full control of the game and should have extended their lead after 57 minutes when Mark Reilly's shot was blocked. Then on 61 minutes Allan Russell got on the end of a Simon Lappin cross and should have done better than head wide.
The same player did make up for this two minutes later when a long free kick was headed back across the goal and he found himself unmarked to easily head home from four yards.
Thistle were offering very little, but substitute Armand One should have given them a consolation on 72 minutes but he headed weakly over from six yards.
As the game was dying out St Mirren scored a deserved third when Reilly carved open the home defence and laid the ball into the path of John O'Neill, who easily beat Arthur low into his far corner from eight yards.