Manager Malky Mackay was left with mixed emotions following Championship leaders Cardiff's side's
He was unhappy at the defending that saw them 2-0 down by the 17th minute.
But he was proud their second-half efforts, particularly those of substitute defender Ben Nugent, 19.
"We put in a spirited second half and we got one back and to be honest we had enough chances to have got the leveller," said Mackay.
However, Mackay was less impressed by moments be believes contributed to goals by Kieron Dyer and Sammy Ameobi scored for Boro.
In skipper Mark Hudson's ankle-injury-enforced absence, defender Kevin McNaughton paid the penalty as he was replaced by teenager Nugent at the break.
"Middlesbrough are one of the challenging teams.
"They were never at home not going to work hard. That's a given in this league.
"We were disappointed with the manner of the two goals we lost, but the spirit of the group meant that we came back and had a real go.
"Yes, we probably did [miss Mark Hudson] today, but I have to say young Ben Nugent came on at half time and I'll take character like that from anyone, never mind a 19-year-old.
"I thought he was excellent in the second half, the way that he came on and showed personality to go on and come into a game like that and really step forward and play against two very experienced forwards and dominate the way that he did."
Mackay felt the efforts of Nugent and his colleagues ensured they were able to strike back through Aron Gunnarsson after the break following the disappointments of the opening period.
And as the Bluebirds sought an equaliser, their manager was left frustrated that none of their chances succeeded.
"I thought we had 10 minutes in the first half where we gave two bad goals away," said Mackay.
"We'd started really well and finished the half really well and second half we gave everything… and really penned in Middlesbrough.
"On another day a couple of those at the end would have dropped in.
"[Cardiff striker] Fraizer Campbell had a header that bounces down and just over the bar and he had the shot where he's hit the guy's hand and the referee's said it's too close for him to give a penalty.
"But the ball's going into the net so on another day it could have been a draw."