Stephen Aitken had scant cause for celebration on his 100th competitive outing in the Dumbarton dugout following an agonising defeat.
Alan Lithgow gave the hosts a richly-deserved advantage during a dominant first period, taking advantage of woeful marking to meet a Nicky Cadden corner and direct a clinical header beyond Scott Gallacher.
Dumbarton were a different side after the break, with Christian Nade striking the underside of the bar, and parity was restored after 75 minutes when Tom Walsh danced into the box to squeeze a shot beyond Neil Alexander at the near post.
However, there was late heartbreak for manager Aitken as Livi captain Craig Halkett latched on to a Lithgow flick-on to convert from close-range.
Lions boss David Hopkin, whose side sit fourth in the Championship, said: “The table doesn’t mean anything right now. This season is about establishing ourselves in the league.”