Pakistan trumped South Africa on Thursday to prove they remain arguably the most unpredictable team in international cricket and former all-rounder Shahid Afridi said it would be a mistake to write them off in the ongoing Champions Trophy.

Four days after being steamrolled by arch-rivals India, Sarfraz Ahmed and his team mates upset South Africa in the rain-hit match to revive their Group B campaign in Birmingham.

Consistency has never been their strong point but Afridi, who has featured in five Champions Trophy campaigns, said the win has the potential to transform the young side.

"It is heartening to see Pakistan play the way it did and I hope it continues its good work and brings smiles on the faces of our passionate cricket fans," Afridi wrote in a column for the ICC's website.

"I also feel that Pakistan shouldn't be ruled out of title contention anymore. The win today can make this side do some amazing things in the tournament. Once again, write Pakistan off at your own peril," he added.

Paceman Hasan Ali led Pakistan's improved bowling performance against South Africa, claiming 3-24 to help restrict the Proteas to 219-8 in 50 overs.

Pakistan were 119-3 in 27 overs, 19 runs ahead under the Duckworth-Lewis method ─ which governs such weather-hit contests ─ when rain intervened to give them their first win in the tournament.

Afridi was particularly impressed with 23-year-old Hasan Ali, who walked away with the man-of-the-match award.

"I don't recall Pakistan fast bowlers delivering match-winning performances in recent years, hence Hasan's three-wicket spell made me really happy.

"He is a mature bowler for his age, has decent pace and the ability of seaming the ball while he can also make the old ball reverse with impeccable control."

Pakistan conclude their Group B campaign against Sri Lanka in Cardiff on Monday.