The Teessiders threw away a 3-1 lead to lose 4-3 to the Welshmen at the Riverside Stadium on Saturday and leave themselves still in the thick of the fight for npower Championship survival.
However, Mowbray insists his side must cope with the loss of the likes of David Wheater to Bolton and Matthew Bates and Justin Hoyte to injury.
"There are a million excuses, but the bottom line is we didn't defend well enough," he told the club's official website.
""It's a much-changed defence - a few weeks ago we had [David] Wheater and [Matthew] Bates, [Justin] Hoyte and [Joe] Bennett.
"I'm not trying to make excuses, it's just the way it is. In football, you have to learn quickly and we are where we are. A couple of weeks ago, we had a different team."
Source: PA
Source: PA