Full-time score from The Den
Christmas may be another month away but a Wiseman in the shape of Barnsley's Scott came early to gift-wrap three points for Millwall with an own goal to settle this drab affair.
There was little to choose between the teams in a scrappy encounter between two sides at the wrong end of the table and desperate for points.
The game seemed to be heading towards a goalless draw when, with 13 minutes remaining, Lions sub Liam Feeney's deep cross was flicked on by Paul Robinson and Wiseman's attempt to clear saw the Barnsley right back send a diving header into his own net.
It was to prove a big three points for Millwall, who moved up to 17th in the Championship table, and vindicated the five changes made by manager Steve Lomas in a bid to find a winning formula for the first time in seven games.
In came midfielder Guy Moussi for his debut, with Mark Beevers, Richard Chaplow, and the two Scotts - Malone and McDonald - all returning from injury.
However, the game saw few clear chances created, the best of which came on 20 minutes when Martyn Woolford cut in from the left and hit a stinging angled drive that Barnsley keeper Jack Butland did well to parry at full stretch.
Martyn Waghorn then sent a left-foot shot harmlessly wide of keeper Butland’s left-hand post as The Lions pressed in patches for an opening goal.
Debutant Moussi latched onto a loose ball as Barnsley failed to clear their lines and saw his long-range left-foot shot charged down. Play immediately swung to the other end and a swift counter-attack by the visitors ended with Marcus Pedersen shooting straight at keeper David Forde.
Barnsley carved out the best opportunity of the opening half when Pedersen teed up Mellis, but the latter saw his low shot saved by Forde with his legs.
The visitors could have been in front after just 33 seconds of the restart when Jim O’Brien sprinted down the right and his cross picked out Mellis at the back post. On this occasion the midfielder's goal-bound header deflected off Justin Hoyte and out for a corner.
Lions boss Lomas introduced Feeney and then Steve Morison in quick succession to try and spark his side into life, and Feeney immediately whipped over a deep cross that Butland did well to hold under pressure.
Wiseman then missed a glorious chance to put the visitors ahead when Malone failed to clear a cross from Tom Kennedy and the right-back nipped in to win the ball, only to see the ball deflected wide for a corner.
At the other end Morison was denied by Butland and then headed wide from another Feeney delivery as Millwall tried to force the opening goal.
And to much to everyone's relief it duly arrived with 13 minutes remaining courtesy of Wiseman's own goal thanks to Feeney's clever wing play and a fine flick on by skipper Robinson.
Barnsley striker Jason Scotland, so often Millwall's nemesis in years gone by, turned his marker with seven minutes left and fizzed a powerful right-foot effort just wide of Forde’s left post.
But in a nervy final few minutes, plus three of injury time, Lomas' charges stood firm to hang on for a morale-boosting and timely victory.
Millwall: Forde, Hoyte, Malone, Robinson, Beevers, Bailey, Moussi, Chaplow (Feeney, 56mins), Waghorn (Easter 90+2min), McDonald (Morison, 61mins), Woolford. Subs not used: Bywater, Shittu, Smith, Martin.
Bookings: Morison (69mins), Bailey (90+2mins)
Scorer: Wiseman (77mins, og)
Barnsley: Butland, Kennedy Cranie, O'Brien, Perkins, Wiseman, Pedersen (Scotland, 65mins), Mellis (Dagnall, 70mins), M'Voto, Etuhu (Dawson, 80mins), McCourt. Subs not used: Hassell, Digby, Cywka, Dibble.
Bookings: McCourt (54mins), Mvoto (82mins)
Att: 9,057 (away 340)