Clashes reported outside the city's Arts Council soon after the unofficial results surfaced. Wahab bagged the top slot of the city with 173 votes, while Jamaat-e-Islami's (JI) Hafiz Naeem-ur-Rehman received 161 as the runner-up.
PPP chairman Bilawal Bhutto and co-chairman Asif Ali Zardari termed the party's victory historic, saying the win became possible due to the struggle and sacrifices of the Karachi chapter workers.
In his message, Bilawal said Wahab and other elected representatives now have a huge responsibility on their shoulders towards resolving the issues of the city.
'Fraud polls'
The JI accused Sindh government of abducting some 29 members of Pakistan Tehreek-e-Insaf, an ally of the party for the Karachi mayor election.
The party demanded that Election Commission nullify the polls and issue a fresh schedule for the same.
Separately, JI chief Siraj-ul-Haq said the process involved the abduction of elected representatives, vote-buying, and pressure tactics.
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In a tweet, he said that people will lose any remaining faith in democracy if the malpractices remain in place.
Haq went on to accuse ECP of colluding with Sindh government, calling it shameful and condemnable. "ECP has lost its credibility with regard to the [forthcoming] national elections."
Several detained
At least eight people were detained after clashes between the supporters of the two parties. Television footages showed unidentified political workers pelting stones at security personnel at the clash site.
The police used batons to contain the situation, with at least two activists receiving injuries. A sit-in was also staged outside the Arts Council where the votes were cast.
PPP Information Minister Sharjeel Memon termed JI a "fascist party", and said no one will be allowed to take the law into their hands.