Brisbane Roar have maintained their excellent record in Adelaide with a 3-1 win over the Reds.
Andrija Kaluderovic opened the scoring for the defending champions in the 26th minute before a Eugene Galekovic goalkeeping howler saw their lead doubled.
Jack Hingert made it 3-0 for Brisbane with his first ever A-League goal in the 54th minute, before Craig Goodwin scored to give United some hope.
A foul in the box saw Daniel Bowles sent off in injury time and Pablo Sanchez converted the penalty to make it 3-2 to the Reds, but there was not enough time remaining for a dramatic comeback.
The Roar improved their record in the city of churches to six consecutive wins.
Adelaide, meanwhile, which would have gone first with a win, remains in fourth place on the A-League ladder.
Meantime, the Central Coast Mariners have edged fellow A-League basement strugglers the Western Sydney Wanderers 1-0 in Gosford.
Josh Rose scored what proved to be the winning goal in just the second minute as the Mariners remained in eighth place, eight points above the bottom-placed Wanderers.