Two second half strikes from Sons’ number nine Ryan Metcalfe, the second a penalty, gave the visitors a shock victory but Rangers were guilty of missing several goalscoring opportunities throughout the 90 minutes and this proved so costly.
Tommy said: “I thought when we looked at how young we would be this year it would be a bumpy ride.
“We’ve had three victories up until now and I think we had enough chances tonight to warrant a victory.
“But it will be a good learning curve for the boys because they were not clinical enough in front of goal and defended poorly at the other end.
“I thought it was a soft penalty they got but in general we need to do better.
“I think we should have won the match but regardless of that we still need to perform better.
“We also need to show a bit more resolve.
“Fraser Aird was outstanding in a Reserve game here two weeks ago and is now in the first team, that’s how close the boys are.
“They maybe feel that and there is a bit of nervousness there but they need to cope with it."
Polish midfielder Kamil Wiktorski was also disappointed after the final whistle but is confident his side can bounce back from this defeat.
He said: "We tried to do our best and play well but, unfortunately, the game did not go as we had planned.
"I think in the first half we had a lot of possession and we should have scored.
"Dumbarton worked hard and then got their reward with two goals.
"So it was not good for us but I hope the next game will be better."