Seoul, South Korea: Chinese title-holders Shanghai SIPG suffered a setback in their quest for a first AFC Champions League crown when they lost 1-0 to South Korea's Ulsan Hyundai on Wednesday.
Brazilian stars Oscar and Hulk, whose late penalty secured last week's 1-0 win over Kawasaki Frontale, failed to inspire a second victory as SIPG dropped off the top of Group H.
Elsewhere in the same group, Manabu Saito's 83rd-minute winner grabbed all three points for Kawasaki Frontale as they beat Sydney FC 1-0.
Oscar, Asia's record signing, had the best chances for SIPG but the visitors were undone by slack defending from a corner when Ulsan's Junior Negrao headed the game's only goal on 66 minutes.
Ex-Chelsea man Oscar's shot from distance, after snapping up a loose ball in midfield, was the best chance of a tepid first half at Ulsan Munsu stadium.
But Ulsan were the more threatening side after the break and the unmarked Negrao put the hosts ahead with a routine header from a corner midway through the second half.
Oscar had another long-range effort palmed away, and Elkeson was denied by defender Dave Bulthuis's superb point-blank block as SIPG pressed for the equaliser.
Oh Seung-hoon saved brilliantly from Oscar as the clock ticked down but there was to be no repeat of last week's late goal against Kawasaki for Vitor Pereira's men.
In Group G, Supachok Sarachart's goal five minutes into the second half proved the difference as Thailand's Buriram United upset 2016 champions Jeonbuk Motors 1-0.
After Supachok struck clinically on the break there was no way back for Jeonbuk, who saw Ricardo Lopes judder the crossbar with a thunderous shot on 69 minutes.