Former Asian title-holders Pohang Steelers took a big step towards the AFC Champions League knock-out phase and dealt Sanfrecce Hiroshima a potentially fatal blow with a narrow 1-0 win on Tuesday.
Bae Chun-Suk's strike on 17 minutes was enough to put the 2009 winners level on points at the top of Group G with both Uzbekistan's Bunyodkor and Beijing Guoan, who fought out a goalless draw in Tashkent.
But the defeat left J-League champions Hiroshima rooted to the bottom with no points from three games, and needing a dramatic change in fortunes if they are to reach the round of 16 as one of the top two teams.
"It is extremely disappointing because our target was just to grab three points. We will go on all out to win all remaining games," said Hiroshima coach Hajime Moriyasu.
FC Seoul survived a late fight-back to beat Japanese visitors Vegalta Sendai 2-1 and extend their lead at the top of Group E, while China's Jiangsu Sainty beat Buriram United to rise from bottom to second in the same pool.
Hiroshima badly needed a win to breathe life into their campaign but they were rocked by the early goal after striker Bae connected with a cross from Go Moo-Yul, who had breached the Japanese side's defence from the left.
Bae was denied a second by Hiroshima goalkeeper Shusaku Nishikawa's foot on 26 minutes, before Park Hyung-Jin came close to converting a chance at the other end.
Pohang, the current K-League leaders, squandered several more goal attempts in the first half, while just before the break Hiroshima midfielder Gakuto Notsuda headed Hironori Ishikawa's cross over the bar.
On the hour-mark, Naoki Ishihara was denied by the width of the post when he met Mihael Mikic's cross and headed off the woodwork.
Bae fired over shortly afterwards and Pohang again came close at the death when Cho Chan-Ho dribbled towards goal and fired off the right post.
"We have no choice but to win the last three matches and keep believing it's possible," said Hiroshima captain Hisato Sato. "We need to throw everything at the last three matches."
In Seoul, the hosts were cruising after first-half goals from Sergio Escudero and Kim Jin-Kyu. But they had to endure an anxious finish after Sendai's Brazilian forward Wilson reduced the deficit with an 87th-minute penalty.
China's Jiangsu had an easier evening in Nanjing after two goals in consecutive minutes put Thai visitors Buriram on the ropes just before half-time.
The hosts were already in the ascendancy when Le Bofei rifled in a rebound on 41 minutes, and they floored Buriram just a minute later when Sun Ke rose unmarked to head home Ji Xiang's cross from the left.
Sun had a second-half effort flagged off for offside as Jiangsu leapfrogged Buriram and Sendai to lie second in Group E, three points behind leaders FC Seoul.
In Tashkent, the competition's first ever game between teams from Uzbekistan and China proved anticlimactic as Bunyodkor and Beijing Guoan played out a 0-0 draw at the new Bunyodkor Stadium.
The result left Bunyodkor, Beijing and Pohang Steelers all on five points with three rounds of games to go in Group G, with Hiroshima still searching for their first point of the competition.
Saudi Arabian outfit Al Shabab top Group A after a 1-0 home win over Tractorsazi Tabriz of Iran.
Qatari side El Jaish are placed third following a 3-1 defeat over UAE's Al Jazira.
Another Saudi team, Al Ahli, stretched their record to a perfect three out of three with a 4-2 win over Iran's Foolad Mobarakeh Sepahan, while Al Gharafa prevailed by an identical scoreline with French striker Djibril Cisse opening the scoring in the 24th minute.
Groups B, D, F and H play their third batch of matches on Wednesday.
The top two from each of eight groups will go into next month's round of 16 in the trans-continental competition, which then takes a mid-year break and does not wrap up until November.