John Sutton’s fifth goal of the season was sufficient to earn the victory and handed Thistle their first defeat in four games at a wintry Fir Park.
Partick won an early corner which was headed narrowly over the bar by Danny Seaborne but their early promise soon faded.
Lionel Ainsworth was then fouled in the Thistle box by Stuart Brannigan and Sutton (14) found the bottom corner from the penalty spot to give Motherwell the lead.
Sutton was inches away from a second and Henrik Ojamaa forced a good save from Paul Gallacher as the home side moved into the ascendancy.
Steven Lawless came on for Thistle at the start of the second period and although the away side improved they were still struggling to carve out any clear-cut chances.
Lawless did well to create a half chance but Dan Twardzik was alert to the danger in the Motherwell goal and the Thistle substitute appealed in vain for a penalty after he tumbled in the area.
Lee Erwin scuttled clear in the last five minutes but was unable to hit the target to make the win more comfortable for the home side.