After retirement, Ōiwa became a coach forKashima Antlers in 2011. In May 2017, he became the new manager, succeedingMasatada Ishii.[2] In the2018 AFC Champions League, he led the team to thefinal againstPersepolis. Ōiwa overcame the absence of five injured players, in addition to the fatigue at the end of the season after playing 52 matches, Kashima Antlers beat Persepolis with two goals in the first leg.[3][4] After a goalless draw in the second leg, the club won the AFC Champions League.[5]