Tokelo Rantie and Percy Tau's second half goals were all Stuart Baxter's men needed to record their first competitive victory over the Super Eagles, and the 18-year-old says losing his first competitive match with the national team was disappointing.
"Every youngster wants to get a win on his debut for both his club and the national team, so, I felt bad we lost that game," Osimhen told Goal.
"But then in football, you expect the unexpected and I still have not got over the defeat because each time I remember the experience, it is devastating for me but I believe the team will bounce back in August when we play against Cameroon."
The 2015 Fifa U17 World Cup winner believes that Gernot Rohr's men will return to winning ways when they battle Cameroon in their Russia 2018 qualifier in August.
"I believe we are going to get the maximum points in that game to make Nigerians happy again, and I also believe the coaches know what to do about the situation to get the job done,'' he continued.
"The fans have the right to be disappointed because we hold a record against South Africa, though records are meant to be broken but I just want to plead on behalf of the team.
"We are pleading with them not to be angry, that we need them more at this time and we are promising that come August and all other teams the Super Eagles will be playing, I believe we are going to get the job done and make them happy in return."