Everyone handled that well. Kelechi originally went over to take it, Sterling said he wanted to as he won the penalty, and Kelechi stepped aside without any real argument. Then Zab stepped in, with the wait of experience and captain's authority and seemed to say to Sterling that Kelechi needed it more (and was likely the designated penalty taker). Sterling stepped away as commanded and when Kelechi put it away he ran over to congratulate him. Then, later, Kelechi spent several chances trying to get Sterling a goal.
That is how it is done.