Match ends, Dumbarton 3, Dundee United 2.
Centre-back Craig Barr scored twice as Dumbarton dented Dundee United's Championship play-off hopes with only their seventh league win of the season.
Calum Gallagher tucked away a cross to open the scoring but Celtic loanee Anthony Ralston headed United level.
Barr rose highest to head home a corner before Scott McDonald's finish again dragged Csaba Laszlo's side level.
McDonald thought he had scored again with a shot which was cleared on the line but another Barr header won it.
His winner from a corner with 10 minutes left earned Dumbarton their first win in five matches and condemned United to a 10th league defeat of the season.
They next host leaders St Mirren at Tannadice on Tuesday with the Paisley side looking to wrap up the title.
United are now nine points behind second-placed Livingston and three behind Dunfermline, having played two games less, but are only two points clear of Greenock Morton in fifth as they struggle to clinch a play-off place.
Dumbarton boss Stevie Aitken: "It was a really good victory for my side as Dundee United are one of the better teams in the Championship and I still think they will fill one of the play-off places.
"The target at the start of the season was to ensure we finished ahead of Brechin City, as we are the two part-time teams in the Championship, and to hope we might get closer to one of the other teams above us.
"Now we are looking to finish strongly with one eye on the fact we do look like finishing in the relegation play-off place. This win says a lot about how hard my players are working."
Dundee United boss Csaba Laszlo: "That was a disappointing result; we dominated the game for large spells but just could not find the way to win. After coming back twice we had one goal chance after another in the last 20 minutes but we could not defend the corners and I am really so sorry for the fans.
"We can only look forward now, but we have lost a very important three points here today. Every single game is a big game for us now but this is a difficult division and every team in it can surprise you.
"At the moment we have to look to reach the third or fourth place, that's now the target and we have to do it."
- 22DickBooked at 57mins
- 3McLaughlinSubstituted forBurtat 78'minutes
- 21HandlingSubstituted forGallagherat 68'minutes
- 7GallagherSubstituted forStewartat 88'minutes
- 16FloodBooked at 5mins
- 28SmithSubstituted forMikkelsenat 64'minutes
- Steven McLean
- Shots on Target
Second Half ends, Dumbarton 3, Dundee United 2.
Corner, Dundee United. Conceded by Liam Dick.
Attempt blocked. Scott McDonald (Dundee United) left footed shot from the right side of the box is blocked.
Andy Dowie (Dumbarton) wins a free kick in the defensive half.
Foul by Thomas Mikkelsen (Dundee United).
Substitution, Dumbarton. Mark Stewart replaces Calum Gallagher.
Attempt missed. Willo Flood (Dundee United) right footed shot from outside the box misses to the right.
Foul by Kyle Hutton (Dumbarton).
Scott McDonald (Dundee United) wins a free kick in the defensive half.
Foul by Calum Gallagher (Dumbarton).
Samuel Stanton (Dundee United) wins a free kick on the right wing.
Goal! Dumbarton 3, Dundee United 2. Craig Barr (Dumbarton) header from very close range to the high centre of the goal. Assisted by David Wilson following a corner.
Corner, Dumbarton. Conceded by Willo Flood.
Substitution, Dumbarton. Liam Burt replaces Christopher McLaughlin because of an injury.
Foul by Samuel Stanton (Dundee United).
Calum Gallagher (Dumbarton) wins a free kick on the right wing.
Attempt saved. Stewart Murdoch (Dundee United) right footed shot from outside the box is saved in the bottom left corner.
Attempt saved. Scott McDonald (Dundee United) left footed shot from the left side of the box is saved in the centre of the goal.
Attempt saved. Scott McDonald (Dundee United) right footed shot from outside the box is saved in the centre of the goal.