Dumbarton gained revenge on Arbroath for two defeats earlier in the season with a late Patrick Walker strike securing a win.
The hosts went ahead after 20 minutes, Bryan Prunty getting on the end of Mark Lemont's cross from the left to head in his ninth goal of the season.
Arbroath levelled soon after through their top scorer Steven Doris, who powered home a Brian Kerr through-ball to notch his 10th of the campaign.
Gavin Swankie played in Josh Falkingham to slot the Smokies ahead before the break.
Stephen Grindlay produced a great reaction save to deny Liam Caddis from extending Arbroath's lead after the interval and Alan Lithgow went down the other end to level for Dumbarton and set up a nervous finale.
Deep into stoppage time, substitute Walker drilled in Anthony Wallace's delivery to snatch Dumbarton's first win in five matches.
Dumbarton: Grindlay, Nugent, Lithgow, Wallace, Creaney, Gilhaney, Nicoll, Agnew (Borris 88), Lemont, Prunty, Graham (Walker 79). Subs Not Used: Brannan, Lyden, Ramage.
Booked: Nicoll, Creaney.
Goals: Prunty 20, Lithgow 84, Walker 90.
Arbroath: Hill, Baxter, Malcolm, Wedderburn, McAnespie, Falkingham (Gibson 79), Kerr, Caddis (Sibanda 75), Sheerin (Brown 90), Swankie, Doris. Subs Not Used: White, Busch.
Goals: Doris 26, Falkingham 32.
Ref: Des Roache