The visitors took a seventh-minute lead through Noh Byung-joon to put themselves in the ascendancy.
Park then doubled their lead in the 52nd minute and struck again in the 58th as the Steelers romped to victory against their title rivals, who slipped four points off the pace.
Ulsan Hyundai managed to stay hot on the heels of the league leaders after holding off Incheon United in their 2-1 win.
Caique Silva Rocha's sixth-minute effort and Kim Shin-wook's strike on the half hour gave Ulsan a cushion and, while Lee Yun-pyo set up a tense finale in the final minute, it came too little too late for United.
Elsewhere, defending champions FC Seoul missed out on the opportunity to move above Jeonbuk after being held to a goalless draw at Busan I'Park.