The world champions wasted no time in securing their bonus point, scoring four tries in the opening 12 minutes.
Scrum-half Reinach bagged an early brace before winger Mapimpi, with his first, and Damian Willemse also crossed.
Reinach sealed a deserved hat-trick from a scrum and Willemse calmly converted as the Springboks took a 33-0 half-time lead.
South Africa started where they left off in the second half through hooker Deon Fourie, who scored his sixth try of the match in the 43rd minute.
Romania’s discipline began to waver and after 54 minutes they awarded a penalty try
Grant Williams scored with two tries before Mapimpi, a handful for the Romanian defense throughout the match, completed his hat-trick with two more tries.
South Africa led 71-0 with 13 minutes remaining and Willie Le Roux came into action in the 73rd minute with the Springboks’ final try of a comprehensive victory to add to their opening 18-3 win over South Africa. Scotland.