Head coach of Adelaide United's Asian Champions League campaign Joe Mullen believes the side's lack of efficiency was their own enemy in last night's 1-0 loss to Sanfrecce Hiroshima.

The Reds could not conjure what they did in their previous three matches which took them into this clash at Hiroshima's Big Arch Stadium with an unblemished record and Mullen pinpointed that it was their inability to take chances which caused the loss.

"We were slow in our build-up in the first half and the movement of our players in the attacking third was also slow and Sanfrecce took advantage of that," he said.

"Sanfrecce were a lot more desperate to win the game in the first half. That was the biggest difference from last week, but we didn't get our players forward as much as we did last week.

"The goal right on half-time was not good. If we could have gone into half-time still 0-0, we could have changed things.

"The second half was a lot better. At the end of the day, we got good chances. At this level against a good opposition; you must take those chances to at least draw, but unfortunately we never did that."

Adelaide still sit at the top of Group H on nine points, equal with reigning champions Pohang Steelers who have a slightly inferior goal difference.

The Reds take on the Steelers at the Pohang Steelyard on Match Day 5 on April 13.