Goals from Marcus Junior and Yotaro Nakajima sealed the points for Michael Skibbe's J-League side against a lacklustre Melbourne City, who were playing in their first game of the new season and presented little threat to their visitors.
Marcus Junior put Sanfrecce Hiroshima in front from the penalty spot in the 52nd minute after being brought down by City goalkeeper Patrick Beach, and Nakajima confirmed the win 10 minutes from time with a header from Shuto Nakano's cross.
J-League Machida Zelvia, making their debut in the competition, secured a 1-1 draw with FC Seoul as Henry Mochizuki struck from close range to earn a point.
The South Koreans had gone in front against the run of play when Jesse Lingard set up Marko Dugandzic to sweep a first-time effort past Kosei Tani in the 59th minute.
But Mochizuki's close-range effort went in off the post after a scuffed attempt by Shota Fujio landed at his feet to earn the newcomers a deserved draw in front of their own fans.
South Korea's Gangwon FC fought back from a goal down to Shanghai Shenhua to win 2-1 at home, with Goo Bon-cheol getting the 63rd-minute winner.
Joao Teixeira had put Shenhua in front with a fine curling effort a minute into first-half stoppage time, but Hong Chul levelled nine minutes after the interval and Goo scored the winner.
Thailand's Buriram United staged a second-half fightback to claim a 2-1 win over visitors Johor Darul Ta'zim.
Cristian Glauder put the Malaysian champions in front from close range in the 28th minute, but Suphanat Mueanta inspired the hosts after the interval.
The Thailand international curled in the equaliser five minutes into the second half and set up Robert Zulj to score the winner from inside the six-yard box.
The matches are the first of eight rounds in the Swiss league phase of the competition, which was introduced last year.
The top eight finishers in the 12-team leagues on the western and eastern sides of the continent advance to March's knockout rounds.