Lennon’s side were comfortably seen off after goals by an own goal, Ross MacLean and Conner Duthie, giving Sons their first opening league victory by a three-goal margin since 1991.
“I would like to start by apologising to the fantastic support that we had here today,” boss Lennon told the club website.
"To wait 16 months and to come in and have to go through that is just not acceptable for the standards that this club sets.
"Yes we are disappointed, yes we are a new team with big turnaround.
"But the signs that we have shown through pre-season, I didn’t see that for long, long periods in the game today.
"At times like that when you see the game going against you that’s when you need your characters, your leaders to organise and I didn’t see a great deal of it.
"This is the worrying thing, it does take time to gel, to connect, but you must always be a one and I felt at times that we were disconnected. In between there, there were one or two whose character shone through when even at 3-0 they were still going.
"But from the standards that we set ourselves and from what I believe in the squad that I have here, it’s a very, very disappointing afternoon.”
By contrast, Sons gaffer Stevie Farrell was understandably thrilled with his side.
He told the Dumbarton website: "It was thoroughly deserved. The two halves were different - in the first, we dominated possession and created several chances, and put together some really good patterns of play.
"In the second - proper footballers manage a 2-0 lead at half time. I thought we were excellent with how we sat in and kept our shape.
"We spoke to Edin Lynch at half time as he was carrying a yellow card, and that was why we took Carlo Pignatiello off late in the game as well.
"Sam Muir wasn't going to face a tougher opponent than David Goodwillie today, but he looked very comfortable on the ball. He stood up really well. I thought all of our back four, and our goalkeeper, were really good.”