The 2012–13 Adelaide United FC season was the club's eighth A-League season. It includes the 2012–13 A-League season as well as any other competitions of the 2012–13 football season, including the 2012 AFC Champions League. Adelaide United will compete in the continental competition for the fourth time, progressing past the Group Stage by topping the group for the third time, thus making the club the most successful Australian club in Asia.
Adelaide United's 2012–13 season was John Kosmina's first full season as permanent coach since being appointed in a caretaker role from Rini Coolen in December 2011. The season was also Kosmina's first in charge at Adelaide since the 2006–7 season. The offseason and preseason saw the signings of Fábio Ferreira from Sydney-based Dulwich Hill FC, Marcelo Carrusca, Daniel Bowles and Jake Barker-Daish. The club begin a new deal with kit supplier Kappa and local solar panel firm Unleash Solar, who joined the club as front-of-kit sponsor.
The club's home and away season began away to Newcastle Jets on 7 October 2012 just four days after being eliminated from the 2012 Asian Champions League. The match saw Adelaide win 2–0, with goals from Dario Vidosic and Iain Ramsay, as well as the debuts of Ferreira, Carrusca, Bowles and Barker-Daish for Adelaide. Adelaide followed this up a week later with a 1–0 win over Western Sydney Wanderers FC in their first away trip, the lone goal to Neumann, thus dealing Western Sydney their first loss and first goal conceded. In Round 3 Adelaide played Melbourne Victory at Etihad Stadium on 19 October. Despite gaining a lead early in the second half through a Vidosic penalty, Melbourne Victory scored two goals for their first win of the season, and Adelaide's first loss.
Adelaide United responded to the loss in kind the following round at home, coming from a goal down to defeat Wellington Phoenix 3–1 in Cássio's 100th A-League match. Aptly, he scored, as did Neumann. In Round 5 Adelaide travelled to Brisbane, continuing their good form at Suncorp Stadium. Dario Vidosic scored from a free kick in just the third minute. Adelaide successfully defended the lead and won the match 1–0, with much notable praise heaped on goalkeeper and captain Eugene Galekovic. Adelaide returned home for a Remembrance Day match against Perth Glory. Perth scored the opening goal, but Adelaide equalised through Vidosic. The match ended 1–1. A week later Adelaide recorded another 1–0 success, this time over Melbourne Heart. Again, the lone scorer was Neumann.
By this point Adelaide had earned its position at the top of the A-League ladder, with five wins, one draw and just one loss. A trip to Sydney at Allianz Stadium on 23 November saw a sixth win against Sydney FC. Ferreira scored his first goal for the club before Yairo Yau equalised. Vidosic struck home the winner in the 88th minute, Adelaide winning 2–1 and continuing Sydney FC's poor form. United's next match was at Bluetongue Stadium against Central Coast Mariners. Eugene Galekovic and Dario Vidosic had been selected to compete for Australia in the East Asian Cup, and therefore did not play the match. However, Vidosic gained an injury and consequently remained in Australia, though he missed the match. Paul Izzo made his debut in place of Eugene Galekovic, becoming the 100th-ever player to make an appearance for Adelaide United. Adelaide gained the lead through Bruce Djite in the 17th minute and led at half-time, but the goal was not enough and Central Coast scored two goals in the second half to hand Adelaide just its second loss in eight games.
A week later Adelaide hosted Melbourne Victory on 7 December. Over 14,000 fans attended, and it proved to be one of the most-watched matches of the season. The match indirectly attracted controversy when reports surfaced of apparent massive, multimillion-dollar bets being placed on the game. Adelaide defeated Melbourne Victory 4–2. Evan Kostopoulos scored his first ever A-League goals, netting a brace, with Ferriera and Carrusca adding to Adelaide's tally. Carrusca scored an astonishing effort, striking the ball with his first touch on the right flank it curved to the inside left of the goal, around Melbourne Victory goalkeeper Nathan Coe. A week later Adelaide notched an eighth win for the season, again defeating Wellington Phoenix 3–1, with a brace to Carrusca and a goal by Ferreira. The final action of the match saw Eugene Galekovic save a penalty, and then athletically save the rebound.