Requiring 207 to win after Pakistan posted its biggest-ever ICC Women’s World Cup total, ICC WWC debutant Laura Wolvaardt (52) and Lizelle Lee (60) set the platform with an opening partnership of 113.
Ismail said: “I looked calm but I was very nervous out there. I just wanted to get it over and done with. It is always nice to contribute with bat and ball, I haven’t’ really done that much in the last few games.
With Pakistan put in to bat first, Bibi represented a crucial presence at the crease as fellow opener Ayesha Zafar (nine) and then Javeria Wadood were bowled by Marizanne Kapp and Moseline Daniels respectively for 43 for two.
With just 20 runs managed inside the second 10 overs, it was looking like hard work for Pakistan.
But Bibi – who was dropped by Ayabonga Khaka on 26 – brought up her half-century off 75 balls to steady the ship.
Bibi’s effort eventually ended when she was run out by Ismail but Pakistan boosted its total later on despite losing Sana Mir and Marina Iqbal off Ismail’s bowling in the final over.
The South Africa openers set about their business well early on with Lee bringing up 1,500 runs in ODI cricket with a six over mid-on before reaching her 10th ODI fifty in dramatic fashion as Sadia dropped a catch at long-on to concede four.
But when Lee and Wolvaardt – who brought up her fourth ODI fifty off 81 balls – were dismissed in the 26th and 31st overs respectively, panic seemed to spread through the South Africa team.
Trisha Chetty (11) was caught at midwicket by Javeria before the latter ran out Kapp (one), Chloe Tryon (three) was bowled by Sadia and captain Dane van Niekerk (two) was another run out victim, this time by Nain, with four wickets lost for 19 runs.
Mignon du Preez then holed out to Asmavia Iqbal at deep midwicket but Ismail held her nerve.
Pakistan captain Sana Mir said: “I think it was a great effort by the girls, the way they fought it out. We lacked in all three departments though.
“We were 20 runs short but the bowlers came chipping in with wonderful overs but there were a couple of missed catches.
“There are areas to improve on but I am happy with the way they fought.”
South Africa beat Pakistan by three wickers at Grace Road, Leicester
Pakistan 206-8 in 50 overs (Bibi Nahida 79, Asmavia Iqbal 27, Nain Adidi 22, Javeria Wadood 17; Moseline Daniels 2-21, Shabnim Ismail 2-52)
South Africa 207-7 in 49 overs (Lizelle Lee 60, Laura Wolvaardt 52, Mignon du Preez 30; Sadia Yousuf, 2-30, Bismah Maroof 1-7)
Player of the match – Shabnim Ismail (South Africa)
Next matches – England v Pakistan, Grace Road, Leicester, 27 June; South Africa v New Zealand, The County Ground, Derby, 28 June