Ten-man Partick lost their grip on top spot after a 3-1 defeat away at Morton.
It was another impressive show from Morton as they ended Partick's unbeaten record and stretched their own winning run to five games.
Kevin Rutkiewicz gave the home side the lead in the 14th minute as he prodded home Michael Tidser's corner from close range.
The lead lasted just six minutes as Steven Craig volleyed in an equaliser from 12 yards out.
Morton re-took the lead six minutes before the break from another corner as Mark McLaughlin scored with a header.
Partick were reduced to 10 men in the 55th minute as Hugh Murray was shown a second yellow for a foul on Stephen Stirling.
And the home side made full use of their advantage as David O'Brien drilled in a low effort from the edge of the area in the 86th minute.