In the initial trends, however, Singh was leading by 194 votes, but Khan later took a huge lead to retain the seat, defeating the BJP rival by a huge margin of 71,827 votes.
In the 2015 assembly polls, the AAP leader had won with a big margin of 64,532 votes.
The party's victory in 2020 polls was on Tuesday celebrated by residents at Shaheen Bagh, the epicentre of the anti-CAA protests, with many offering free food and 'biryani' to people.
Hectic polling was recorded till late afternoon in the five polling stations at Shaheen Bagh and those at Jamia Nagar, also another centre for protests against the amended citizenship law.
Okhla constituency had, however, recorded 58.84 per cent turnout.
Shaheen Bagh has been the epicentre of anti-CAA protests in Delhi, running into over 50 days now.
Protesters had taken turns on polling day on Saturday to cast votes to keep the agitation alive.
Looking to capture power after a gap of 22 years, the BJP had mounted its one of the most aggressive campaigns in the Delhi Assembly polls, with Union Home Minister Amit Shah leading the saffron charge fuelled by its planks of Hindutva and nationalism, and its strident opposition to Shaheen Bagh protests.
The issue often dominated the political discourse during the campaign, with many BJP leaders targeting the ruling AAP and the Congress, accusing them of "misleading people" holding anti-CAA protests in Delhi.
In a near-repeat performance of 2015, the AAP on Tuesday retained power with a stunning victory, winning 62 of the 70 assembly seats and leaving the BJP with just eight seats.
The AAP had bagged 67 seats in 2015.
Patparganj sitting MLA Manish Sisodia, after winning his seat again, said the BJP indulged in "politics of hate", but people refused its agenda.
Khan in January had said that he would conduct a low-key poll campaign and not take out any road show, bike rally or pad yatra in solidarity with the ongoing protests against the amended citizenship act and NRC.
In a video message, the sitting MLA from Okhla had said that he would also file his nominations quietly as two major protests -- one at Shaheen Bagh and another at Jamia Milia Islamia -- were taking place in his constituency.
"I will not take out any road show, bike rally or pad yatra in solidarity with the ongoing protests against the amended citizenship act and the NRC," Khan had said.
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