Relegation-threatened Dumbarton held on for a vital three points in a see-saw win against in-form Livingston.
Dumbarton, who lost 4-3 at home to the same opponents last week, took a fourth-minute lead when Brian Prunty latched onto an Scott Agnew cross to finish from the edge of the penalty area.
But Livingston levelled after 22 minutes when Jordan Morton finished neatly from close range.
A minute later Dumbarton regained the lead when Andrew Graham tucked in another good Agnew cross.
Livingston equalised on the stroke of half-time when the lively Iain Russell was fouled in the area by Jamie Ewings. Russell picked himself up to emphatically rifle home the penalty, his ninth goal of the season.
Dumbarton took the lead for the third time with a 69th-minute Agnew penalty after Prunty was tripped, but they had to play the closing minutes with 10 men when Mark Gilhaney was dismissed for foul and abusive language.
Mullen struck the post from 12 yards for Livingston in the 85th minute as the away team hung on.
Livingston: McNeil, McCann, Garcia Tena, Barr, Booth, Kyle Jacobs (Mullen 76),O'Brien, Andreu, Scougall, Iain Russell, Morton (Ross Gray 81). Subs Not Used: Jamieson, Watson, Fordyce.
Goals: Morton 22, Iain Russell 45 pen.
Dumbarton: Ewings (Grindlay 90), McGinn, Lithgow, Graham, Smith, Gilhaney, Turner, Agnew, Lamont (Lister 61), Prunty (Creaney 82), Fleming. Subs Not Used: McCusker, Thomson.
Sent Off: Gilhaney (79). Booked: McGinn, Prunty, Lister.
Goals: Prunty 4, Graham 23, Agnew 69 pen.
Ref: Paul Robertson