Luiz Henrique opened the scoring midway through the first half, firing home a rebound after Kim Byung-ji saved Cho Sung-hwan's shot.
The Brazilian was involved in the second just after the half-hour as he was adjudged to have been fouled in the area by Seo Sang-min and Lee Dong-gook made no mistake from the spot.
Henrique then netted the third after 36 minutes, sweeping home a loose ball from close range.
Four minutes before the break, Kang Sung-jo gave the hosts hope with a fabulous free-kick curled into the top corner of Jeonbuk's net.
"It's been a tough week with an away game in Japan and then an away game here," said Jeonbuk coach Choi Kang-hee.
"We talked about approaching the game in the right way mentally and getting a good start early in the match."
Earlier in the day, FC Seoul secured a last-gasp 2-1 win over Busan I'Park.
Eder Baiano headed Busan into the lead at the end of the first half but Kim Dong-jin scored a rare goal after 63 minutes to pull Seoul level.
In the final minute, Choi Tae-wook slipped the ball through to Kang Jung-hoon and he scored from inside the area.
Suwon Bluewings stay in fourth as Mato Neretljak scored the only goal of the game at bottom club Gangwon FC.
In the day's other fixture, Jeju United and Chunnam Dragons drew 1-1. Kim Myung-jung put Chunnam ahead before Kim Eun-jung equalised for Jeju.