League leaders Gretna looked anything but as they came under pressure for the majority of the remainder of the first half with defender Allan McManus heading into Main's hands from 6 yards and Mensing heading over from similar range.
The second half had barely kicked off when Gretna took an undeserved lead as Ryan McGuffie powered home a Gavin Skelton cross.
St Johnstone hit back quickly though as Scotland cut a swathe through the Gretna defence before having the presence of mind to set up Paul Sheerin who clinically dispatched the equaliser past Main from 12 yards.
St Johnstone scored next after great work on the wing from full-back Goran Stanic whose cross was headed in strongly by Martin Hardie.
Gretna manager made a tactical switch in the 68th minute bringing on Matthew Berkeley and Kenny Deuchar. The attacking manoeuvre paid dividends in the 76th minute with the equaliser coming from Berkeley's incisive run following which the ball broke to Eric Paartalu who smashed the ball into the top right hand corner of the net.
In the 84th minute Gretna grabbed the lead after Simon Mensing handled a Danny Grainger cross and McGuffie struck the resultant penalty.
This amazing match ended with Scotland smashing home a free-kick from 25 yards to give his side a share of the points.