Lescott saw red for a high challenge on Barnet's Dean Sinclair, with the scores at 1-1, but Rovers held on to keep their play-off hopes alive.
The visitors dominated most of the first half but saw Jason Puncheon's free-kick on the stroke of half-time cancel out Richard Walker's early opener.
Rovers' top scorer Walker took just 12 minutes to net his 18th of the season, heading in a wicked Stuart Campbell free-kick in off the underside of the bar.
The visitors should have had three by the break, with Lewis Haldane dragging wide and Craig Disley shooting straight at the keeper when clean through.
Barnet finally woke from their slumber with 10 minutes of the half to go, with a Liam Hatch header forcing a stunning save from Steve Phillips and Adam Birchall dragging just wide.
Puncheon's sweet left-footed free-kick came just before half-time, the midfielder giving keeper Phillips no chance after Hatch had been fouled on the edge of the box.
The game changed just after the break with Lescott's sending off, but the home side could not capitalise.
Birchall should have scored when he beat his marker to a Puncheon cross, and was through again after Steve Elliott missed the ball, but his weak shot was easily smothered by Phillips.
Barnet continued to pour forward but could not find a goal that would have given them a fourth consecutive win.