United have now drawn eight of their last nine league and cup fixtures but Houston is encouraged by how difficult his team have become to beat.
Saints led through Darren McGregor's 37th-minute header but three minutes from time substitute David Robertson nodded United level.
Houston said: "These guys just never know when they're beaten and I think it would have been totally undeserved if we'd lost that game. We put everything into it and created good chances, the problem was that we went behind in the game again.
"We have to eradicate the fact we're chasing games from behind. If we can get in front with the same application and attitude, I think we can start winning games.
"We're on a run of draws but you're delighted to come to places like these and get something sometimes because we've come out of losing a game and got a point through showing character. We've had a few late comebacks this season but this was frustrating in that we had clear-cut chances to have scored much earlier in the game."