I think Pakistan decided to bowl by winning the toss today keeping in mind the second match. And they were able to prove that their decision was not wrong in the first over. Shaheen Shah Afridi dismissed two reliable South African batsmen on the second and third balls of the first over and gave away three runs including a wide in the first over. I will not say right away that Pakistan will easily win today's match because the game is in the T20 format and in this format if one or two batsmen can bat well, a team's total can reach a fairly good place. I think the South African team has enough good batsmen, if they can form a good partnership, they can make a fairly good total. Later, the bowlers can take the game to an interesting level by bowling well.
Today I think Muhammad Waseem Jnr. deserve the chance to play, he is always used to be the part of crucial series, matches or even such events but he is being dropped and dropped no matter Shaheen , Naseem, and Mirza are more good bowlers and if we check the history of Muhammad Waseem Jnr. so he is all average, he never performed such good way and never performed in such worst way.
However, in the first over Shaheen was being unplayable with the new ball used to swing the ball in that way batters cannot judge his style and technique of bowling.