Former champions Muang Thong United and Port recorded important Thai League 1 victories to wrap up the first leg on a high on Saturday night.
Muang Thong, outplayed 3-1 by league leaders Bangkok United in a fiery battle last week, bounced back with a 4-1 home victory over Nakhon Ratchasima.
Port, meanwhile, continued their recovery under new coach Sarawut Treephan, extending their winning streak to three matches in the top league by beating Nongbua Pitchaya 1-0 in an away game.
The Kirins were shot ahead by prolific Willian Popp just three minutes into the match and their advantage was doubled by Korawit Tasa 20 minutes later.
With two goals in their pocket, all Muang Thong had to do was to keep the Swat Cats from kickstarting a comeback and their defenders were up to the task last night.
Poramet Arjvilai put the things out of Nakhon Ratchasima's reach, adding the third to the home team's tally after 75 minutes.
Chalermpong Kerdkaew pulled one back for the visitors, but Willian struck again in the dying moments to make it 4-1 for the Kirins.
Muang Thong ended the 15-game first leg with 25 points from seven wins, four draws and an equal number of losses.
Sergio Suarez gave Port the winner in the 38th minute for a victory that boosted their hopes for a finish among the top four teams in the league.
Nongbua's bid to claw their way into the match suffered a big blow 10 minutes before time when Airton Tirabassi was sent off by the match referee for a foul on Suarez.
The result brought to an end an admirable seven-game unbeaten run for Nongbua, who were promoted to the top flight for the first time in the club's history this season.