The Reds were good money for their 1-0 lead at half-time thanks to Marlon Harewood's 23rd minute strike, but a late headed goal from McDonald gave Middlesbrough a share of the points.
Paul McShane saw red in his final game for Barnsley in the 72nd minute and Boro were able to take advantage of having an extra man to draw level with six minutes of the 90 remaining.
Barnsley set off in search of their second Championship double of the season and it was a bright start from both sides. Taylor flashed across the six yard box in the opening stages but no red shirt was on hand to tap home.
A moment later Hill cleverly played in Harewood only for his pullback to be cleared by Boro - it was a great piece of play down the Barnsley left.
Another good Barnsley build-up saw Mellis slip in Haynes for a one two with Harewood but Haynes was denied by the flag - Mark Robins' side were looking very lively going forward.
The Reds broke the deadlock on 23 minutes through Marlon Harewood. Persistence was key as his initial header was saved by Smith, but he managed to scramble home after regaining control of the ball.
Barnsley were controlling the game with Butterfield and Mellis combining well as Doyle protected the back four. The first real chance fell for Taylor of Boro on 32 minutes after McDonald's delivery, he just couldn't make a connection at the far post which would surely have been an equaliser for the home side.
Shackell had to clear off the line as Boro broke down the centre, a ball out to the left found McDonald who lofted the ball to the far post only for the skipper to knock clear.
Danny Haynes was booked for pulling back Joe Bennett as he looked to break into the area with 39 minutes gone - the resulting free kick was hammered wide by Robson.
The former Bristol City man could have then doubled Barnsley's lead after stealing into the area, but the striker failed to make a connection from Mellis' chip.
Butterfield allowed Harewood to burst forward down the left - his cross was tipped away by Smith and it almost fell for Gray in the area.
Middlesbrough were probing and almost got in through McDonald with two minutes gone after the break - he flashed another cross across Barnsley's six-yard area but yet again nobody was there for Mowbray's men. A minute later and Rhys Williams got a shot away from 15-yards but Shackell - who is surely in the running for Player of the Season - managed to get in a crucial block.
Barnsley broke on 52 minutes and Haynes was denied by a terrific challenge from Bennett. Hill then tested his shooting boots but volleyed wide after intercepting another poor Boro pass.
Steele was tested by Robson from 20-yards after Halliday's corner fell kindly to the midfielder - but Barnsley's number one got down well to tip wide for corner on 54 minutes.
Hill then had a header smartly saved by Smith on 57 minutes. The former Wolves man was found in the area by Trippier's expertly-delivered free-kick but Smith gathered neatly at his near post.
Flood was introduced for Boro at Halliday's expense as Mowbray looked to inject some sort of imagination into his side with over an hour gone.
Haynes was in down the right and had acres of space to create a Barnsley second - his delivery took a nick on its way through to Harewood and Haynes couldn't convert the rebound. Mellis found Butterfield who then drilled wide from 25-yards after it opened up for the Bradford-born midfielder on 67 minutes. It was simply a delight to watch the two Jacobs combining in midfield.
It all kicked off on 72 minutes as Bennett reacted angrily to McShane's challenge - the Hull City loanee was given his marching orders after a mass melee near the technical area. Thomson was only booked for the home side.
After a break in play following the fracas - Mellis was replaced by Stephen Foster and Jim O'Brien came on for Danny Haynes.
The home side then made their remaining two changes, Tarmo Kink and Richard Smallwood came on for Barry Robson and Kevin Thomson.
Bennett then tested Steele but the Reds' stopper was comfortable in gathering his 25-yard effort. It was Barnsley's turn to attack once again, Harewood was in on Smith but the former Forest stopper denied the striker his and Barnsley's second. The Reds certainly weren't resting on their one-goal lead; the ten-men wanted more.
Kink really should have levelled on 82 minutes but headed over. A minute later and the equaliser did come, despite Barnsley's superiority throughout the game. It was McDonald with a free header, making no mistake from 10 yards.
Butterfield was then cynically hauled back by Williams as the Reds looked to counter down the left and five minutes of added time were indicated by the fourth official. Butterfield then had an effort deflected wide as Smith was completely stranded after flapping at Hill's free-kick.
Yet again the Reds were denied the points they deserved - but to come away from the Riverside disappointed with a point shows just how far the club has progressed over the past few years.
Smith, McManus, McDonald, Thomson (Smallwood 74), Davies, Robson (Kink 74), Halliday (Flood 60), Williams, Taylor, Bennett, McMahon
Sub not used: Coyne, Haas, Grounds, Tavares.
Steele, Shackell, Trippier, McShane (sent off 72), Hill, Doyle, Haynes (O'Brien 73), Mellis (Foster 72), Butterfield, Harewood (Arismendi 90), Gray
Subs not used: Preece, McEveley, Clark, Taylor.
Referee: C D Sarginson
Assistant Referees: M J Denton & P Hodskinson
Fourth Official: R J West
Attendance: 16, 107 (668 away)