The commentators at the Rangers Celtic match claimed the fixture was the oldest in football. I was very dubious because I though Celtic were not in competitive football in the early days.
I got out my history books and noticed that in a competitive match - The first derby with teams still playing today ( In either England or Scotland ) was a third round Scottish FA cup fixture , between Rangers and Partick Thistle
Date 1878 -79
Rangers went on to get to the final at Hampden, drew 1. 1 with Vale of Leven. Rangers failed to turn up for the replay claiming they scored the winning goal in the first match which was disallowed. The SFA awarded the cup to Vale.