Bruno Fernandes opened the scoring from the penalty spot after Rasmus Hojlund was fouled by Blues goalkeeper Robert Sanchez, only for Moises Caicedo to equalise for the visitors four minutes later.
The result leaves United 13th in the table, with just 12 points from their first ten matches.
Meanwhile, their total of nine goals is their fewest at this stage of a league campaign since 1973/74, a season which saw them got relegated from the old First Division.