United, leading 2-0 from the first leg in Holland, looked home and dry when Javier Hernandez opened the scoring after six minutes, but replies from Aras Ozbiliz and Toby Alderweireld left the hosts clinging on. United boss Sir Alex Ferguson blamed himself for picking a defence lacking in experience. He said: "I picked too many young players in the back four positions – that was a big problem in terms of experience. It was a big risk I took.
"Ajax are fantastic in terms of keeping the ball. Their first goal I thought was a handball in the build-up, but although they had a lot of possession they didn't look like scoring.
"But that goal gave them confidence and we only had one shot in the second half. I thought we were very poor in the second half."
Defender Phil Jones said: "We got off to a great start, scored and seemed to be in control of the game.
"But a little bit of complacency set in. We should have won the game comfortably."