Groups B and C began today at the age-group tournament, which offers three places for the men's Olympic Games competition at Tokyo 2020.

The Saudis beat 2016 winners Japan 2-1 at Thammasat Stadium in Rangsit, after Abdulrahman Ghareeb fired home an 88th-minute penalty in the Group B clash.

Makoto Okazaki had fouled Feras Al Brikan in the area, with the spot-kick confirmed by the video assistant referee system.

Ayman Al-Khulaif's first-time finish had given Saudi Arabia the lead on 48 minutes, but Ryotaro Meshino replied eight minutes later with an effort which took a huge deflection to leave keeper Mohammed Al Yami wrong-footed.

There was also late heroics in the other Group B game, as Syria battled back from 2-0 down to earn a draw with Qatar.

Alaa Aldin Dali converted at the back post with four minutes played in added time to earn a share of the spoils after an entertaining encounter.

There was also an early goal as Qatar's Yusuf Abdurisag tapped home with less than a minute on the clock after Syrian keeper Yusuf Abdurisag fumbled the ball.

Syria continued to be architects of their own downfall when Yosief Mohammad scored a 22nd-minute own-goal, but they gained a foothold nine minutes later thanks to Abdul Rahman Barakat's header.

In Group C, Lee Dong-jun scored in the third minute of added time to earn South Korea a 1-0 win over China at Tinsulanon Stadium in Songkhla.

The substitute latched onto a long pass and stroked home a finish to prompt wild celebrations on the Korean bench.

Defending champions Uzbekistan had to settle for a 1-1 draw with Iran in the group's other game.

Islomjon Kobilov scored a 40th-minute penalty to give the Uzbeks the lead after Bobir Abdixolikov was brought down by Mojtaba Najarian.

Reza Dehghani levelled with a close range finish shortly before the hour mark and the points were shared.

Group D begins tomorrow with matches between Vietnam and United Arab Emirates and North Korea and Jordan.

As Japan have already qualified for Tokyo 2020 as hosts, the remaining three semi-finalists will book their Olympic places should they reach the last four.

If not, the two finalists and the winner of the third-place playoff will advance.

The top two teams in each group will reach the quarter-finals, with the final scheduled for January 26 in Bangkok.

Men's Olympic football features under-23 sides, although three overage players are allowed in the final squads.