South Korea closed out a 2-1 triumph in Prague to send 10-man Czech Republic into Euro 2016 pondering a ragged defeat.
Pavel Vrba's team came into the match on the back of friendly wins against Malta and Russia over the past nine days but they found their latest visitors an altogether tougher proposition.
Petr Cech should have done more to stop Yoon Bit-Garam from opening the scoring with a free-kick from the right-hand corner of the penalty area and the impressive Suk Hyun-Jun made it 2-0 at the break.
Basel defender Marek Suchy was one of four half-time replacements for the Czechs and reduced the arrears almost instantly with a deflected long-ranger.
Theodor Gebre Selassie almost equalised before being sent off for a second bookable offence after an hour.
Czech Republic remained on top despite their numerical disadvantage but were unable to draw level, with thoughts now turning towards a testing Group D opener against reigning European champions Spain on Monday week.
Vrba's men gradually pushed their opponents back early on and Jung Sung-Ryong made a good low save when veteran midfielder Tomas Rosicky looked to beat him at his near post.
South Korea withstood a spell of pressure, with Ladislav Krejci's attempt blocked from close range, and they silenced the Eden Stadium crowd by taking a 26th-minute lead.
Gebre Selassie was booked for cynically bringing down Suk on the counter-attack and Yoon dispatched the resulting free-kick, although Cech is unlikely to view replays of him pushing the chipped effort into his top-left corner with any fondness.
Looking to atone for his part in the opener, Gebre Selassie played Krejci into the box but the Sparta Prague winger dragged his shot across goal, while Rosicky failed to match Yoon's exploits from a dead-ball opportunity.
In the 39th minute, Czech full-back Pavel Kaderabek hooked a bouncing ball back from the byline for Tomas Necid to glance wide before Korea's attack shone once more.
Yoon turned provider, slipping a well-timed pass into Suk's path, and the Porto forward thumped an unerring finish beyond Cech, who had no chance on this occasion.
Suchy made an impact within a minute of his introduction as a speculative 30-yard strike took a decisive deflection off Korea captain Kwak Tae-Hwi to leave Jung wrong-footed.
The replacement centre-back almost followed his maiden international goal with a second five minutes later when he leapt unmarked to head over from Vladimir Darida's set-piece.
Korea were under siege and Jung showed sharp reactions to tip a Gebre Selassie shot against the base of his far post.
But the Werder Bremen left-back would have no part to play in the final half-hour, with a foul on Jung Woo-Young earning him a second booking.
Still, Czech Republic pressed and Jung Sung-Ryong made his best save of the match, at full stretch to thwart Tomas Sivok from 10 yards.
There were further acrobatics from the Korean keeper in the 75th minute, as Jiri Skalak turned a cross from fellow sub David Limbersky goalwards, and Uli Stielike's men held out.
