Boro took a two-goal lead with goals from Joel Byrom and Scott Laird before substitute Richard Cresswell's header gave United hope of mounting a comeback. After Kevin McDonald put a drive narrowly wide, Matt Lowton struck in the 85th minute to set up a tense finish.
Smith said: "Credit to my players for the way they held on at the end in the face of some strong pressure.
"It's a fantastic point. We played some very good football and deservedly went 2-0 up. But their first goal lifted them and their fans really got behind them. The momentum shift was very visible.
"It was a fantastic atmosphere and they certainly finished the stronger. In the end we were probably hanging on a bit. It's back in our hands again. It gives us control over what happens next week. We've got to win our home game to get in the play-offs.
"The teams fighting for that sixth place remain the same. Anything can happen. If we can win, we have the trump card with the goal-difference which will take us into the play-offs."