South Africa prevailed by six runs in a tense finish after being sent in and making 192 for six.
De Kock slammed 83 off 58 balls as South Africa chased down a target of 241 with seven wickets and ten overs to spare to seal a 3-2 series win.
"Whatever happened has happened," Sarfraz told media at the airport after landing from Cape Town.
This is also the first time ever Pakistan won an ODI against South Africa at the Wanderers
Shoaib Malik will lead Pakistan in the remaining two ODIs and the subsequent T20I series against South Africa
The Pakistan captain later apologised for the comment on Twitter.
Pakistan will play a three-match T20 series against South Africa after the completion of undergoing five-match ODI series
Imam's 101 spurred Pakistan to an imposing 317 for six but South Africa won by 13 runs according to the Duckworth/Lewis/Stern method