Pakistan struggled to 129 for eight after being sent in, with only two batsmen reaching 20 against South Africa's all-pace attack on a hot, humid evening in which the bowlers were able to swing the ball and get movement off the pitch.
But any demons in the pitch seemed to disappear as Smith and Bosman went on an all-out attack.
They took South Africa to 132 for no wicket off only 11.3 overs. It was the highest partnership in the short history of 20-overs internationals.
Smith smashed 71 not out off 40 balls with nine fours and four sixes, finishing the match with a six off Shahid Afridi, while Bosman was unbeaten on 53 off 32 balls with five fours and two sixes.
The two sides meet again on Sunday at Centurion in the first of a five-match one-day series.
Smith said his bowlers had set up Friday's win.
"There was a little bit in the wicket with the new ball and I thought we bowled superbly," said the skipper.
New cap Alfonso Thomas, who took a wicket with his first ball in international cricket, took three for 25.
Smith, playing in his fifth 20-overs international, became the first batsman to score three half-centuries in the shortest form of the international game.
"Loots and I had a bit of fun," he said. "There was a short boundary on one side which we tried to cash in on. Loots got the momentum started and I just carried on with him."
The two innings were in complete contrast, with the Pakistan batsmen struggling against the South African bowlers.
A last over which brought 18 runs, including two sixes by Rana Naved-ul-Hasan off Johan van der Wath, gave Pakistan some hope, which was quickly extinguished by Smith and Bosman.
Stand-in Pakistan captain Younis Khan said he did not believe the comprehensive beating would influence the outcome of the one-day series. "We have just come from Test cricket and we had a lot of changes, with new boys coming into the team who are not used to playing in South Africa."
Pakistan looked set for a good total when Kamran Akmal (21) and Mohammad Hafeez (25) put on 47 off 35 balls for the second wicket.
But Hafeez chipped a catch to cover off the last ball of Shaun Pollock's four-over spell and Pakistan quickly lost two more wickets, while Shahid Afridi had to retire hurt before he had scored after he was hit in the groin by a ball from Roger Telemachus.
Afridi returned at the fall of the fifth wicket but made only seven off 17 balls before being caught off a wild slog against Thomas, who gained impressive away swing and showed good control.
A rain interruption at 76 for four after 11.4 overs was another setback for the Pakistan innings.
The last over provided the drama of the innings. Naved-ul-Hasan was dropped when he swung at Van der Wath and top-edged the ball.
Wicketkeeper AB de Villiers ran back but could not hold the chance. It proved costly because Naved slammed the last two balls of the innings over square leg for six to finish with 17 not out off seven balls.
Pakistan captain Inzamam-ul-Haq, still struggling with a back injury he suffered in the final Test in Cape Town, sat out the match in the hope of being fit for the first one-day international.
Leading batsman Mohammad Yousuf and fast bowling discovery Mohammad Asif were both rested.
South Africa rested several of their key players, including Jacques Kallis, Mark Boucher, Makhaya Ntini and Andre Nel ahead of the one-day series.
Pakistan 129 for 8 in 20 overs (Mohd Hafeez 25, Kamran Akmal 21, Nave-ul-Hasan 17 n o; Alfonso Thomas 3 for 25, Morkel 1 for 16, Telemachus 1 for 22, Pollock 1 for 26) lost to South Africa 132/0 in 11.3 overs (Graeme Smith 71 n o, Loots Bosman 53 n o) by 10 wickets