"I was the first to vote. I have voted for the same one, always the same one," the lemonade seller in his 50s told AFP.
Taxi driver Ozcan Ege also glowed with praise for Kasimpasa's favourite son.
Ege, 65, grew up in the neighbourhood and remembers Erdogan as a "hard-working" and "intelligent" teenager, predicting he will win with 60 percent of the national vote.
"But here he will have 90 percent," he said.
Erdogan defied expectations when he almost secured an outright victory in the first round on May 14, making him the clear favourite to extend his two-decade rule to 2028.
He has frequently played up his humble roots in the hilly neighbourhood on the European side of Istanbul, which neighbours a much richer one where the secular opposition dominates.
"I learned life in Kasimpasa, not in an ivory tower," Erdogan said earlier this week as campaigning for the runoff election drew to a close.
'No one like Erdogan'
Yasar Kirici, 80, was the neighbour of the future president. "He came by the front of our door every day. He was a great lad," he said.
The man supporters reverently call "Reis" ("chief") visited Kasimpasa just before the first round and "greeted us from his car", Kirici said with a smile.
"He doesn't come here a lot anymore. He doesn't have the time, he's busy sorting the world's problems," he added.
A short distance away, Ilyas Arslan served soup to a recently arrived client. "There's no one like Erdogan -- he's like a dad to us!" enthused the man in his 50s, clad in a white apron.
Textile worker Mustafa Siper said Kasimpasa electors would vote "100 percent" for Turkey's longest-serving leader.
Secular challenger Kemal Kilicdaroglu, the head of a six-party opposition alliance, "can't win", he concluded.
But not everyone in Kasimpasa is a fervent follower of Erdogan and his Islamic-rooted party.
Sitting outside his shop with a steaming cup of tea, Hasan Kirci once vied with Erdogan during games of street football -- this time he's opposing the 69-year-old at the ballot box.
Kirci, 70, said he opted for Kilicdaroglu because a local football pitch was closed and "now all the youngsters are taking drugs".
His neighbour Recep Ozcelik, 75, will also vote for Kilicdaroglu, blaming Erdogan for a severe cost-of-living crisis.
"How much does a kilo of cheese cost now?" fumed the retired driver, complaining about the difficulties of eating meat like he used to.
Kilicdaroglu is also making inroads among Kasimpasa's younger voters, including 30-year-old Ramazan Parlak.
"He's a democrat, he's an honest man," Parlak said of the opposition leader. "Turkey has become Afghanistan. If Erdogan wins, I will leave for Germany or France."
Sitting at a nearby bus stop, Kaan Karababa, 25, fears that an Erdogan re-election will be disastrous for Turkey.
"The economic crisis will get worse and refugees will continue to come in masses," he told AFP.
But taxi driver Ege dismissed the economic troubles plaguing Turks. "Inflation isn't a problem, people always have a little money," he said.
Despite a slight limp in his walk and a more haggard face, Erdogan managed to maintain his relentless campaigning, holding up to three rallies per day.
"He's not too old," Ege insisted. "Maybe he's a little tired, but that's normal, he works day and night."