alright in the circumstances, the 3rd Hokage (God of Shinobi) was old and not in his prime, Orochimaru was full power fighting him with Edo Tensei, the 3rd beat the Edo tensei and Orochimaru in his old age, so imagine him in his younger years in his prime, he'd kick konohamaru's ***, and konohamaru can't beat Oro, Oro has tons of jutsu and konohamaru does'nt really have many jutsu, plus do you really think the 3rd would keep falling for the sexy jutsu?
Konohamaru's strongest move is rasengan, do you really think the 3rd would'nt see that coming from far away, hiruzen is a fire and earth style, and he got the monkey god Enma, how can you say Konohamaru can beat him? Hiruzen is faster and stronger even in his olden days. The monkey god Enma can kill konohamaru with one hit, and Enma is incredible fast and dont remember Hiruzens ultimate jutsu, konohamaru is finished.
Konohamaru might be lucky and surpass him one day, but he is barely kissing hiruzens feat, plus konohamaru is not that smart and he is reckless, rushing into battle.
Hiruzen Sarutobi (God of Shinobi) > Konohamaru Sarutobi (Learned rasengan by naruto)