United were denied a clear penalty and had a goal disallowed, which would have changed the face of the game dramatically and Walter Smith told Setanta Sports that Rangers knew the game would be extremely difficult to navigate.
"We've got to expect that at this time of the season for any of the teams there is a lot at stake for them now," Smith admitted.
"So, you've got to give them credit for pushing forward in the second-half of the game.
"From my own point of view it's a difficult thing for us while they could push forward we had our fourth game in nine days and one of them had extra-time to handle and everything, so it would be expected that the teams who are pushing for a cup place would put us under pressure at some stage or other.
"Dundee United came into the game in the last 15 minutes of the first half and that was maybe a sign of things to come.
"When they go 2-0 down at this stage in the season there's nothing in it for them if they don't win the game.
"And in the second-half they pushed forward, I felt we had a little bit of fatigue there in terms of managing to keep control of the ball and we lost a lot of opportunities to break on Dundee United that we might have done better with, but in saying that a tremendous effort from all our boys."