Amakhosi will meet Orlando Pirates in the PSL's flagship fixture at FNB Stadium on Saturday.
"Everyone is watching and if you don't play well you going to be bad but if you play well, you will be the most talked about person in the country," Mphela tells snl24.com/kickoff.
"I mean the Derby in this country is like that... it can make or break you."
The Royal Eagles forward has advised the Derby debutants to try and relax and embrace the occasion.
"It is a most wonderful game to play and everyone is watching, and it comes with pressure," he adds.
"I think to the new players they have been professional for long now. For them they have to relax and try to enjoy the occasion. It is a beautiful occasion for the whole country.
"So for them they should go there and enjoy the occasion."
'Killer', who left Chiefs in June, is joint-third on the NFD scoring charts with four goals, behind Baroka's Thabiso Kutumela (seven goals) and Cleopas Dube (five goals) of Witbank Spurs.