It was announced on 1 December 2011 that as part of the
AFC Champions League review conducted earlier in the year, Australia would be granted an extra play-off slot for the 2012 edition of the competition. Adelaide United placed 3rd in the
2010–11 A-League season and thus gained entry into the Play-off stage of the competition, alongside Champions
Brisbane Roar and Runners-Up
Central Coast Mariners who qualified directly into the Group Stage. Due to the Chinese and Indonesian clubs' withdrawal from the play-offs, Adelaide were fortunate enough to be drawn directly into the Group Stage of the
2012 AFC Champions League without the need to progress through the preliminary stages. The club was drawn into Group E alongside former opponents,
Gamba Osaka,
Bunyodkor and
Pohang Steelers.
February In an unprecedented turn of events, the
Court of Arbitration for Sport ruled in favour of rebel Indonesian club
Persipura Jayapura’s appeal for inclusion in the competition and revoked Adelaide's direct entry into the group stage and a play-off match was reinstated to determine the club to progress to Group E. Adelaide United hosted the Indonesian club on 16 February, and convincingly won the game 3–0, therefore removing all doubt of the club's right to enter the continental competition for the Australian club record 4th time.
March On 6 March, Adelaide United travelled to
Tashkent,
Uzbekistan for Match Day 1 of the Champions League, and returned with a 2–1 win in sub-zero conditions against reigning Uzbek champions,
Bunyodkor. Former Asian champions,
Gamba Osaka made the trip to Hindmarsh Stadium for Match Day 2 on 20 March. Adelaide United came out the victors with a first half brace from
Daniel Mullen being the difference. On the back of the club's win over Gamba Osaka, interim head coach
John Kosmina was signed on for a further season as the club's manager on 22 March.
April Match Day 3 saw Adelaide United travel to the home of
Pohang Steelers on 3 April, where a rare defensive error from Adelaide captain and goalkeeper
Eugene Galeković gifted the home side the sole goal of the contest, and the three points. The return leg was played in Adelaide two weeks later, where again a lone goal decided the tie. On 18 April, Adelaide United kept its second clean sheet of the AFC Champions League group stage when
Bruce Djite scored in the 90th minute to send the Australian club clear at the top of Group E.
July The club announced a new 2-year partnership with kit supplier
Kappa on 16 July, after it dissolved its previous contract with
Erreà after the company's failure to deliver products to the club's expectations.
August Without
Coopers Brewery as primary major sponsor, Adelaide United were forced into securing an alternative major sponsor. On 29 August, the club announced a one-year front-of-shirt sponsorship partnership with Unleash Solar worth a reported $250,000. ==Players==