DUBAI: Son Heung-min's South Korea needed an extra-time winner to beat world ranked 113th Bahrain 2-1 as they stumbled into the Asian Cup quarter-finals in unconvincing fashion on Tuesday.
Kim Jin-su's diving header at the end of the first extra period proved the difference as the two-time champions met unexpected resistance before winning in Dubai.
But Paulo Bento's side, runners-up in 2015 and one of the favourites for the title, survived to reach the last eight, where they will face Qatar or 2007 winners Iraq.
Tottenham star Son took a boot to the head as he weathered some robust challenges in a first half which South Korea dominated with 73 percent of possession.
Bahrain nearly stunned the Koreans with Mohamed Marhoon's stinging early shot as South Korea took time to settle into their rhythm.
But from the half-hour Son started to make his presence felt with some typically direct running which caused panic in the Bahrain defence.
South Korea broke the deadlock two minutes from half-time, when Son laid off to Lee Yong whose cross was parried by the goalkeeper to Hwang Hee-chan, who snaffled the easy chance.
South Korea threatened to run riot after the break before Bahrain hit back and it took a magnificent flying stop from Kim Seung-gyu to keep out Jamal Rashed's thumping effort.
And against all expectations, Bahrain were suddenly level with 13 minutes remaining when Mohamed Al Romaihi smashed in the rebound from Mahdi Al-Humaidan's shot.
The goal stunned South Korea, who had only conceded twice at an Asian Cup game since 2011 — the 2015 final, which they lost 2-1 to Australia after extra time.
Hwang Ui-jo nearly snatched the victory in injury time, when a defensive mix-up put him one-on-one with Sayed Shubbar Alawi, but he spooned his shot wide to set up the additional 30 minutes of play.
South Korea's first goal had been their only shot on target but they looked determined to put that right and substitute Lee Seung-woo should have done better when he was set up in the box by Son's strong run.
Bahrain goalkeeper Alawi withdrew with an apparent hamstring injury but one of the first tasks for his replacement, Abdulkarim Fardan, was to pick the ball out of the net.
Substitute Kim Jin-su found time and space to steady himself and drive home a header from Lee Yong's cross, a goal which the team celebrated by holding up the 16 shirt of injured Newcastle United midfielder Ki Sung-yueng.
Ju Se-jong also rammed a shot against the post in a positive finish for the Koreans, and while they celebrated there were tears from the Bahrainis at the final whistle.