There was more disappointment for Thistle when they went down 4-1 at Tannadice on Saturday.
Dundee United were on top form with their first goal coming in 90 seconds. Ryan Gauld, who would torment Thistle throughout the game, spotted Gary Mackay-Stevens to his left and he placed a shot beyond Thistle goalie Scott Fox and into the back of the net.
The remainder of the first half was a pretty one-sided affair and Thistle were fortunate in the extreme not to be trailing by more than that early goal by half-time.
Thistle only started to come into the game in the 56th minute when they were handed a lifeline. Ross Forbes shot at goal was clearly being handled inside the box by Souttar and Aaron Muirhead confidently slotted home the resultant penalty.
For a spell immediately after that goal there was the prospect of even better to come from Thistle. James Craigen found room at the edge of the United box but his shot lacked power and Paul Paton was fortunate to receive only a yellow card for a late challenge on Taylor-Sinclair as Thistle stepped up the pressure.
United, however, were back in front in the 69th minute. Andrew Robertson got in behind the Thistle defence down the United left and he buried a low drive past Fox.
In the 74th minute the game took a decisive turn in United favour when Conrad Balatoni collected a second yellow card leaving Thistle to complete the match with 10 men.
United wasted no time in taking advantage of this with Gauld slipping the ball through to Mackay-Stevens who netted his second goal of the game with 14 minutes remaining.
Christie Elliott responed with a shot that was deflected wide as they tried to stage an unlikely comeback, but the game’s final goal came at the other end with Brian Graham firing high into the back of the Thistle net in the 84th minute.