With Barnsley sitting a goal to the good with 21 minutes left courtesy of Marlon Harewood's first half opener, McShane decided to go stupid over very little on Teesside.
He was unhappy with how Kevin Thomson complained about a challenge near the touchline and then the Barnsley centre-back's row with the Boro man sparked a rush of blood from everyone on the pitch except for Scott McDonald and Paul Smith.
McShane, who looked as if he had directed a punch at one stage, also started on Joe Bennett, who was heavily involved along with Andrew Taylor and Jacob Mellis. But it was the instigator who deservedly saw red.
And McDonald's decision to channel his energy in other directions were vindicated six minutes before time when he headed in the equaliser from substitute Tarmo Kink's cross.
The point may not have been enough to secure Championship football for next season, but Middlesbrough know that can be done if they extend an unbeaten run to eight at Burnley on Tuesday night.
Middlesbrough were forced to make five changes to the team that drew at Ipswich in midweek, but the early signs were positive when Andy Halliday embarrassed McShane before his centre was cleared when an early opener looked on.
But when Robins changed things by asking Harewood to play wide left and Danny Haynes to switch to the right, the visitors soon enjoyed more success going forward.
And he got his reward in the 23rd minute when a half cleared corner fell nicely for full-back Kieran Trippier. The unmarked Trippier had time to pick out Harewood at the back post and the striker's shot deflected in off Andrew Davies despite goalkeeper Paul Smith denying the first attempt.
Apart from Harewood's late surge on half-time, when his low drive was turned behind by Smith, it was Middlesbrough that created the better chances, but failed to do anything with them.
Taylor's back post volley, after a decent centre from Tony McMahon, rolled wide after being helped on by McDonald, while Barnsley skipper Jason Shackell did well to head an Halliday chip off the line.
With Middlesbrough losing, Mowbray attempted to change things by hauling off Halliday. But with a lack of alternative options through injuries and suspensions, midfielder Willo Flood was asked to be the second striker for a time.
McShane made things interesting 20 minutes from time. He had no reason to react the way he did, pushing and shoving before clearly throwing a punch as everyone got involved.
McDonald was one of only two players the other being Smith not to be involved and then six minutes from time the Aussie rose in the box to flick Kink's delivery inside the far post.
MIDDLESBROUGH (4-4-2): Smith; McMahon, McManus, Davies, Bennett; Robson (Smallwood 74), Williams, Thomson (Kink 74), Taylor; Halliday (Flood 62), McDonald. Subs: Coyne (gk), Haas, Tavares, Grounds. BARNSLEY (4-4-2): Steele; Trippier, McShane, Shackell, Hill; Haynes (O'Brien 70), Doyle, Mellis (Foster 72), Butterfield; Gray, Harewood (Arismendi 90). Subs: Preece, McEveley, Taylor, Clark.