Dumbarton earned promotion to cinch League One after a 2-2 draw with Spartans resulted in a 4-3 aggregate win for the Sons in their play-off final.The visitors held a narrow 2-1 advantage after Tuesday’s first leg and simply needed to avoid defeat to win promotion, but fell behind after just three minutes at Ainslie Park,  when Cameron Russell nodded home Callum Booth’s cross.Celebrations were short lived, however, after Michael Ruth fired in the equaliser just two minutes later, then completed his brace eight minutes into the second half.Blair Henderson coolly converted from the spot in the sixth minute of stoppage time for Spartans but they could not find another.