United surprised many at Old Trafford by holding the reigning European champions to a draw, with Nemanja Vidic's header cancelled out by a Bastian Schweinsteiger strike.
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But Robben insists the result should not be a surprise, given United's defensive approach to the match.
"It was not easy, as our opponents didn't leave any gaps," he told the German press.
"We wanted to play football but they tried to stop us. The English were just playing on the counter and have played very defensively, it was almost like in handball.
"But when you go a goal down you have to be pleased with a draw. 1-1 is a very good result that we can take home with us and then we just have to finish it off next week."
Team-mate Toni Kroos added: "It was difficult: we were dominant all the time. It's very difficult to play against a team that consistently has all its players around their own penalty area."
But club captain Philipp Lahm remains confident Bayern will see off United at the Allianz Arena in the second leg. "We wanted to win here, but if you come back from 1-0 down you can be satisfied," he insisted.
"It puts us in a good starting position."
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