Lawrence Shankland scored his first goal for Dundee United but it didn’t lead to a victory.
The former Ayr United man made his debut on Friday night off the bench against Brechin City but he was given a start at Dumbarton.
His close-range header on 58 minutes cancelled out an opener from Jim Duffy’s side three minutes into the second half.
United found themselves behind again on 65 minutes but it was 2-2 when Louis Appere was fouled in the box and then converted the penalty kick himself.
Dumbarton took the lead for a third and final time after Mark Reynolds was dispossessed.
All three of their goals were scored by trialists.