Nadir Ciftci, who had an early long range effort saved by Alan Mannus, crafted the opener midway through the first half as Erskine fired home from 12 yards into the bottom right-hand corner.
From keeper Radoslaw Cierzniak’s throw upfield, Ciftci used his pace to set up Erskine who netted with a crisp finish.
Steven Anderson and Michael O’Halloran both went close for the visitors who enjoyed a little more possession and had just as many efforts on goal as the league leaders.
The closest they came was via O’Halloran who struck a post just before the hour mark from a tight angle.
But 18 minutes from time Paton sealed the three points with a low shot from inside the box after latching on to Keith Watson’s measured assist.
Saints continued to press but to no avail as United safely saw the game out to earn a measure of revenge for their Scottish Cup final defeat back in May.
And with Inverness losing at Aberdeen, United are now two points clear at the top.