Clark was pleased with Birmingham's battling performance after twice coming from behind to earn a point.
He admitted: "Chris Burke changed the game for us after a disappointing first half only to concede another bad goal.
"We were then staring down the barrel but Kyle Bartley came up with the goods after going on as a late substitute.
"He has pestered me to allow him to go up front and he came up with the goods in terms of a great header from a set-piece.
"We are now unbeaten in five games. It is a good little run which shows we have solidarity.
"We would love to win but when you are going into injury time a goal behind you willingly take the point from the draw.
"Bartley is effective from set-pieces and we knew we had the height advantage when he went on late in the game.
"He is a very good athlete. He is quick and he can pass the ball. You see the size of him and when he attacks the ball it is very difficult for anyone to mark him.
"I was gutted when he had to come out of the team and now he is pushing to regain his place in the side.
Burke, however, was Birmingham's saviour as he won the penalty which his fellow Scot, Phil Caddis, scored in the 57th minute to cancel out a 22nd-minute strike by Mustapha Carayol.
Middlesbrough appeared to be heading for a long overdue win at St Andrew's when Daniel Ayala scored in the 80th minute.
But it was Burke who again engineered Birmingham's late equaliser with an accurate corner which Bartley headed home four minutes into injury time - just four minutes after coming on as a late substitute.
Middlesbrough, who had only once in their previous 15 visits to St Andrew's desperately need to find some winning away form.
Their failure to beat Birmingham means they have only won once in 23 games on their travels and picked up just seven points.
Middlesbrough's newly installed manager, Aitor Karanka, was equally disappointed and frustrated.
The Spaniard said: "We were playing and working very well only to lose everything in the last minute.
"We need to improve in this period of the match and not to concede such vital goals.
"We are only four points above the relegation zone and not in a very comfortable position.
"When I arrived the most important thing is getting the points as it makes the players and myself more confident.
"It is not the first time it has occurred - but we have made mistakes late in the game.
"This is the second time in a few days that we have lost vital points. We know it is a problem and we were aware before the game that Birmingham are very good at set-pieces.
"At half-time I told my players that we needed a second goal to win the game but Birmingham played very well in the second half to score two goals and earn a draw."