North Korea, the lowest ranked side at the East Asian Cup, came back from a goal down to stun holders Japan 2-1 in the opening match in Yuhan on Sunday.
Japan and South Korea have sent domestic-based players for the four-nation round-robin tournament which is not officially recognised by FIFA. Due to its non-official status, European clubs have not released their players ahead of the start of the season.
North Korea, ranked 129th in the world compared to the 50th ranked Japan, took full advantage of the absence of AC Milan's Keisuke Honda and Shinji Kagawa of Borussia Dortmund in mounting a late challenge in the second half to complete the victory.
South Korea, who are also missing Bayer Leverkusen's Son Heung-min and Ki Sung-yeung of Swansea City, however, had a comfortable 2-0 win in the day's late match against hosts China with goals from Kim Dae-seung and Lee Jong-ho.
Japan, held to a goalless draw by lowly Singapore in their opening World Cup 2018 qualifier in June, looked set to give a better account of themselves against North Korea when debutant Yuki Moto gave them the lead after just two minutes.
But Vahid Halilhodzic's men failed to convert their chances after that, paving the way for their opponents to equalise through Ri Hyok Chol in the 78th minute and then Pak Hyon Il scored the winner with two minutes remaining. "We were not prepared physically but we had chances and could not take them," Japan coach Halilhodzic was quoted as saying by the Kyodo news agency. "They sent a two-metre-tall player (Pak) on and scored with the two chances they had. Our players looked tired and we could not keep up physically." China's defence kept frustrating South Korea for long before midfielder Kim opened the scoring in the last minute of the first half.
Lee increased the lead 12 minutes after the interval.
Uli Stielike's side will face Japan in their next match on Wednesday while China take on North Korea.