Pohang Steelers were too strong for Busan I'Park on Sunday, while Gangwon rallied from a half-time deficit to open the new K League season in style.
Stanislav Iljutcenko opened the scoring midway through the first half but the home team were made to wait to seal the points, Serbia midfielder Aleksandar Palocevic eventually doubling their lead from the penalty spot in the 71st minute.
Australian midfielder Brandon O'Neill was an unused substitute in the 2-0 victory.
Meanwhile, Seoul finished third in the 2019 campaign and duly took the lead at Gangwon, Park Dong-jin's deflected shot finding the net to put the visitors ahead at the break.
However, the hosts hit back in the second half, starting with substitute Kim Ji-hyun converting a cross to level.
They then secured the 3-1 victory with two late goals, the first of them scored by Cho Jae-wan with a clever back-heeled finish.
Having created his side's second, Kim Seung-dae sealed the result less than a minute later, cutting inside onto his right foot to score with a low finish.