Urawa Reds, looking to win the Asian championship for the second time in three years, suffered a huge setback in their Asian Champions League round-of-16 opener, a 2-1 home loss to South Korea's Ulsan Hyundai on Wednesday.
Hwang Il-su stroked the 80th-minute winner as the visitors came back from a goal down to take control of the fixture with two away goals ahead of next Wednesday's second leg at Ulsan Munsu Football Stadium.
Reds, the only J. League team with two Asian titles, dominated first-half possession at Saitama Stadium but had to settle for a lone goal in the 37th minute from a Kenyu Sugimoto header.
Joo Min-kyu, however, equalized five minutes later when he headed home a cross from Lee Keun-ho.
"We anticipated a tough game but the players really gave their all," Ulsan head coach Kim Do-hoon said. "Our aggressive play opened the door for us to come from behind. Now we need to prepare diligently for the home leg."
The hosts were playing their first ACL game under interim manager Tsuyoshi Otsuki, who took over on May 28 after the firing of Oswaldo Oliveira.
"When it comes to controlling the game for 90 minutes, there are still many things that we have to do," Otsuki said.