Thai League 1 sides Port and Muang Thong United both lost the first leg matches in the last 16 of the AFC Champions League Two on Thursday night.
Port suffered a 4-0 humbling at home against Korean side Jeonbuk Hyundai Motors while hosts Muang Thong narrowly lost 3-2 to 10-man Lion City Sailors from Singapore.
Andrea Compagno scored twice (24th, 60th minutes) while Park Jin-Seop (19th) and Song Min-Kyu (49th) were also on target for Jeonbuk as the former AFC Champions League winners all but booked their berth in the quarter-finals.
The Korean side are now in total control ahead of next Thursday's second leg at Jeonju World Cup Stadium.
Lee Seung-Woo played a short corner to Lee Young-Jae, who sent a cross towards the far post, from where Compagno looped his header back to Lee Seung-Woo and his nod down was swept over the line by Park Jin-Seop from two yards out in the 19 minute.
Five minutes later, Lee Seung-Woo's initial cross from the left was swung back into the danger zone by Park Jin-Seop and Compagno made no mistake with a downward header that beat Port goalkeeper Somporn Yos.
Jeonbuk moved further ahead in the fourth minute of the second half as Song Min-Kyu headed in their third goal.
Compagno claimed his second of the night 11 minutes later as he powered another header beyond Somporn after being found by Kim Tae-Hwan.
Coach Wasapol Kaewpaluk blamed lack of focus during dead ball situations for Port's downfall but promised his team would try their best to overturn the deficit.
"It is disappointing because we conceded two cheap goals from set-pieces," said Wasapol. "It made the game even harder for us as we had to chase the game.
"But we tried and when you do that, you leave yourself more open and that's how we conceded another two in the second half. It's going to be even harder now in the second leg but we will still fight when we go to Korea."
At Thunder Dome Stadium, Shawal Anuar, Maxime Lestienne and Bart Ramselaar all scored inside the opening 27 minutes to give Lion City a blistering start to the tie but Song Ui-Young's red card seven minutes after the restart almost undermined their efforts.
Melvyn Lorenzen pulled one back for the hosts in the 59th minute and Tristan Do scored with the final touch of the game in the 100th minute to set up an intriguing return clash at Jalan Besar Stadium next Thursday.