On the morning after, Corey O’Connor stood with his wife, Katie, on a corner in their Pittsburgh neighborhood. Each cradled a toddler in one arm — she carried Molly, he carried Emmett — and in the other arm held up a handmade sign that read “Thank you, Pittsburgh.” Passers-by waved and honked.

That gesture on Wednesday morning was how Mr. O’Connor chose to thank the voters who a day earlier had sent him to victory in the Democratic primary for mayor of Pittsburgh.

It was also a familiar one. Mr. O’Connor’s father, Bob, had done the same thing when he won the Democratic primary for mayor in 2005, standing on a street corner with a hand-drawn thank-you sign — finally on his way to the city’s top office after two failed attempts.

For many Pittsburgh residents, the ascent of the younger O’Connor, 40, surely rekindled memories of his father, a champion of the city who was diagnosed with brain cancer six months into his term and died weeks later.

“Corey has it,” said Bruce A. Kraus, who served on the City Council with Mr. O’Connor. “Corey was weened at his father’s heel. He’s got a good heart and a good moral compass.”

In a city that hasn’t had a Republican mayor since one was appointed in 1932, Mr. O’Connor is heavily favored to win the general election in November against the Republican nominee, Tony Moreno. Still, Mr. O’Connor’s ascent represents a notable turn for the city and the party, four years after Ed Gainey rode a wave of pandemic-fueled progressivism to defeat two-time incumbent Bill Peduto in the Democratic primary.