Young defender Stephen Harvey received his marching orders as Lynn's play-off hopes suffered a major blow in the Midlands.
Harvey was dismissed for deliberate handball late in the first half and Halesowen duly took advantage by putting away the resulting spot kick.
The 20-year-olds sudden rush of blood leaves the Linnets with a mountain to climb in the final three weeks of the season.
Manager Tommy Taylor said: "I don't know why he did it.
"The ball was going beyond the back post and he has just punched it outside the six-yard box. The forward was behind him, but there was no need to do it.
"Stephen is a quiet lad at the best of times, so I didn't have to say too much to him afterwards."
Taylor added: "I was disappointed with us in the first half. I felt a couple of the players were off the pace and at this stage of the season we need all 11 out there on the pace.
"You can't blame the heavy amount of games of late because we were still going strong in the latter stages against Team Bath and the players had a week of light training."
The attack-minded Taylor, who played two at the back and three up front after the interval, said: "I thought we shaded the second period, but with only 10 men Halesowen were always going to have their fair share of breakaways."
Lynn had penalty claims off their own turned down in the first half when the ball appeared to strike the arm of a Halesowen defender.
Striker Darran Hay did have the ball in the net 10 minutes before the break, only for the offside flag to deny him.
Sam McMahon fired wide and a Mark Angel corner was also off target from Hay in an off-colour first 45 minutes from Taylor's side.
Halesowen missed two golden opportunities to increase their lead at the start of the second half before the Linnets finally began to threaten.
A Jack Defty header was well saved by Chris Taylor before the home keeper was on hand to foil Danny Bloomfield shortly after.
Halesowen's Jimmy Haarhoff should have put the game beyond Lynn's reach late on, but twice wasted half chances.
Halesowen: Taylor, Skidmore, Haywood, Preston, Amos, Smith, Cowley, Moore, Lamey (Haarhoff 68), Baker, Forsdick. Subs not used: Gayle, Pope and Johnson.
Lynn: Wilson, Camm (O'Halloran 80), Blake (Quistin 50), McMahon, Hammond, Clark, Defty, Harvey, Hay (Staff 65), Bloomfield, Angel. Subs not used: Forshaw and McAnally.
Referee: Mr S. Robins (Bristol)
Bookings, Halesowen: Forsdick (dissent); Lynn: Defty (foul).
Sent-off: Harvey (deliberate handball).