Thai Premier League champions Buriram United are in danger of elimination after losing 2-1 at South Korea's Seongnam in the AFC Champions League yesterday.
In the other Group F game, Japan's Gamba Osaka won 5-0 at Guangzhou R&F.
Seongnam have 10 points, while Buriram and Gamba each have seven and Guangzhou have four after five matches.
In the final round of matches on May 6, Buriram host Guangzhou and Seongnam travel to Gamba.
The top two teams of each group progress to the next round. If two or more teams finish on equal points, the ranking will be determined by results between the teams involved.
At Seongnam, first-half goals from Kim Do-Heon and Nam Jae-Joon gave the hosts a 2-1 win over Buriram.
Seongnam were on top for most of the game at Tancheon Stadium after a penalty from Kim and a Nam header set them on course for victory, but a late goal from Buriram's Brazilian striker Diogo ensured a nervous end to the game for the hosts.
Following a cautious start to the match, Seongnam took the lead on the 27th minute.
After an exchange of headers in the area, the ball fell to Kim just outside the box and his low shot was handled by the sliding Narubodin Weerawatnodom.
The referee pointed to the spot and Kim coolly slotted the kick into the net.
Seven minutes before the break Seongnam moved further ahead. Kim whipped a free-kick from the right into the penalty area and Nam was unmarked to head high into the net.
The Thai champions started the second half with determination, and pressured the hosts with a couple of corner kicks, but soon Seongnam, two time continental champions, re-established control of the game.
However, with 13 minutes remaining, the Thunder Castle pulled a goal back.
A deep right-sided corner kick was headed back across goal by Karnwit Narmwiset and Diogo was there to head home from close range.
Despite late Buriram calls for a penalty due to a handball, Seongnam held on for a vital and deserved win.
In Group E, goals from Brazilian Eduardo and Kosuke Taketomi helped Kashiwa Reysol overcome former winners Jeonbuk Hyundai Motors 3-2, and claim top spot in the group, as they secured their passage to the last 16 round with a game to spare.
Japan's Kashiwa took a 3-0 lead at half-time, but the Koreans came out strongly after the interval and scored twice through captain Lee Dong-Gook — who is now all-time leading scorer in the AFC Champions League with 27 goals.
Despite a late rally, Kashiwa were able to hold on to advance to the next stage.