The Red Devils failed to defend a 96th minute corner which allowed Michael Obafemi to score an equaliser.
And Maguire says United must defend better if they want to compete for titles.
Speaking to Sky Sports, Maguire said: "Very disappointed. We got ourselves in a great position to win the game but then invited pressure on ourselves by not being very good on the ball. We knew we would have to grind the results out sometimes.
"When you are down to 10 men the one thing you can do is defend set plays, get your head in it and get the ball out of the box but we didn't do that. We can't be doing that if we want to get to where we want to get to.
"The way we try to play and try to build from the back there are times we might get caught on the ball and we have to react quickly. The boys reacted brilliantly. We had numerous chances to finish the game off. The second half we had to be better on the ball, disappointing in the end.
"There is definitely no complacency - great group of lads. We knew it would be a tough game, felt we did enough to win the game but we didn't. Big games between now and the end of the season and hopefully we can get to where we want to get to.
"We want to be playing for titles. I am sure the boys will dust themselves down and we have a big game coming up next."