Reds snatch the points in Roses battle: Blackpool 0-1 Barnsley
McGeehan struck on the hour mark to end a four-game winless run in League One and move ahead of Doncaster and into the top six.
The Reds edged a tight first half and could have led with Brad Potts teed up Mamadou Thiam from a quick counter-attack, but the attacker did not make a clean connection.
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Hide AdAdam Davies then produced a good save at the near post to deny John O'Sullivan, but still Barnsley pressed and Kieffer Moore uncharacteristically missed a free header at the back post.
Potts, returning to his former club, could have broken the deadlock early in the second half but he dragged his shot wide.
But he could not be kept out the action and he played a part in the decisive moment of the game, setting up McGeehan.
He sent in a delightful cross, allowing his midfield partner to head home at the far post.
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Hide AdCauley Woodrow almost made it two deep into injury time, but their lead was never threatened as the play-off positions beckon for Daniel Stendel's men.
Barnsley: Davies, Cavare, Lindsay, Pinnock, Pinillos, Potts, McGeehan, Mowatt (Dougall 90), Thiam (Bahre 80), Moore, Woodrow (Adeboyejo 90).
Subs: Greatorex, Moncur, Jackson, Brown.
Blackpool: Howard, Daniels, Heneghan, Tilt (O'Connor 46), Feeney (Guy 75), Spearing, Pritchard, Bola, Thompson, O'Sullivan (Nottingham 70), Gnanduillet.
Subs: Delfouneso, Boney, Davies, Bunney.
Referee: Anthony Backhouse
Attendance: 4,054