The Koreans have won the regional tournament on each of the last three occasions it has been played, and the victory moved Bento's team level with tournament hosts Japan at the top of the early standings.
An own goal from Zhu Chenjie gave the Koreans the lead six minutes before the interval, with Kwon Chang-hoon adding the second from close range in the 54th minute before Cho Gue-sung completed the scoring 10 minutes from time.
South Korea have qualified for November's World Cup finals in Qatar, where they will play Ghana, Uruguay and Portugal, but Bento has not selected any of the country's Europe-based players for the east Asia competition.
They were facing a Chinese side that has been built around the country's under-23 squad and are being led by Serbian coach Aleksandar Jankovic.
The inexperienced Chinese held out until the 39th minute when central defender Zhu sent a looping header into his own net despite not being under any pressure to clear Kwon Kyung-won's punt forward from near the halfway line.
Kwon Chang-hoon added the second nine minutes into the second half, slotting in from close range after Kim Jin-su's header back across the face of goal.
The Koreans went further ahead in the 80th minute as Goh Young-joon's inch-perfect pass behind former Everton defender Tyias Browning - known as Jiang Guangtai in China - released Cho and he stroked the ball under goalkeeper Han Jiaqi.
Japan handed Hong Kong a 6-0 thrashing in their first game of the competition on Tuesday, and the hosts will take on China in the next round on Sunday while the Koreans face Hong Kong.
The final round of matches will take place on July 27 when China take on Hong Kong and Japan play South Korea.