Doolan’s early goal proved more than enough to ensure Thistle will be in the top half of the Ladbrokes Premiership after the split and guarantees their highest finish since they came sixth in the league 36 years ago.
Thistle dominated the first half against a disjointed Motherwell side, who were again without injured top goalscorer Louis Moult. But they faced long periods of pressure after the break as the much-improved visitors pushed forward in numbers without creating many clear-cut chances.
Stephen Robinson’s side dropped below Hamilton into the play-off spot on goal difference and face a huge game at home to bottom club Inverness next Saturday.
Motherwell set about trying to press Thistle high up the park but they gave them far too much room in their defensive third in the 11th minute as Doolan grabbed his 102nd goal for Thistle, and few can have been simpler. Chris Erskine peeled off to the left and had time to deliver a straightforward low cross for the striker to stroke home from six yards without any pressure.
Both teams were playing a 3-5-2 formation but Thistle looked much more comfortable and they regularly had Motherwell on the back foot thanks to incisive passes forward from Adam Barton, Steven Lawless and Ryan Edwards.
The visitors were fortunate to go in just one behind at half-time. Barton came close from a free-kick, Lawless saw a shot deflected on to the top of the bar after getting one-on-one with Carl McHugh, and Doolan curled wide from a great chance after Edwards had played the ball inside Elliott Frear at the end of a slick passing move.
It was clear Motherwell needed to make changes at half-time. Lionel Ainsworth and Keith Lasley came on for Frear and Craig Clay as Robinson switched to a flat back four.
The substitutes brought some much-needed vitality to Motherwell’s play and they began to pen Thistle inside their own half. Debutant Shea Gordon saw his ball across goal just evade the back post and the visitors thought they had levelled when Zak Jules met Ainsworth’s deep free-kick and headed towards the corner of the net in the 70th minute. But Tomas Cerny clawed the ball away as Well claimed it had gone over the line.
Lasley shot just over from 20 yards and Motherwell brought on a third striker, Jacob Blyth.
However, Thistle continued to defend their box well from a number of corners and crosses as they moved seven points clear of Kilmarnock to get their top-six place with plenty to spare.