"The difference here I think now is the belief in the team. They just played it out on the ground and the team believes in itself," said Mullen.

"There is a difference from the A-League season. There is a real sense of belief, want, desire, commitment, tenacity all those kinds of things.

"Seventy-five minutes there was still time to get something back. Tonight, the game, when they went 2-1 down they showed they've got the spirit and desire."

The Reds are all but guaranteed a place in the round of 16 with three wins in as many games and a three-point lead over Pohang Steelers in Group H.

"It means a lot (the win). It sets us up to finish off the group stage with a top two position, but of course we'd like to finish top so we can get a home game in the round of 16. However, we haven't achieved anything yet, we still haven't qualified." Mullen said.

The win means Sanfrecce are still rooted to the bottom of the group and is yet to record a point.

The Purple Archers boss Mihailo Petrovic denied Sanfrecce was out of contention for the ACL round of 16 despite losing all three of its group games so far.

"There are positives and negatives for the match and it depends what the players will take from it. I'm not sure of the results of the other teams so we'll just go back and wait for the revenge on Tuesday (return fixture in Japan)," he said.

Marcos Flores starred for United in the first half before running out of legs in the second. Sanfrecce then began to take control in the midfield, scoring twice and taking the lead before a double substitution from the Reds' bench saw them regain composure.

Goal-scorer Robert Cornthwaite was quick to acknowledge the difference made by Cassio and Fabian Barbiero when they came on to replace Flores and Lucas Pantelis with 20 minutes remaining, before emphasising the theme of belief within the squad.

"The players that came on gave us a lot of energy and the will to go on and win," he said.

"It's just a really strong belief amongst the boys at the moment. If someone had said that (top of Group H) at the start, you know obviously we had faith in one another and believed we could do it.

"At the same time, these teams that we're coming up against, Asian champions Pohang Steelers, Shandong, the Real Madrid of China. These teams that we're coming up against aren't easy teams and I think the way we've approached every game with a fantastic attitude, full of confidence and I think that's why we're in the position we are in."