Since the national tournament's start on Thursday, Iaconelli - a 42-year-old Philadelphia native - had caught 37 pounds of stripers by the end of Saturday, putting him in the lead.
But sitting on stage Sunday in a replica of a bass boat seat was Chris Lane of Guntersville, Ala., the new leader, with a four-day catch of 39.2 pounds.
Iaconelli would need a catch just a fraction over two pounds pounds to win the tournament and its breathtaking first prize of $100,000.
"Ten pounds, 14 ounces!" M.C. Dave Mercer cried, and the crowd of about 500 standing on the concrete steps around the stage cheered, pumped fists, and howled, "Ike! Ike! Ike!"
"You didn't just beat the competition, you crushed it!" Mercer shouted.
Iaconelli wiped his face as though in disbelief, broke into a broad smile, and bowed so low to crowd his fingers brushed the stage floor.
"Oh, man, this is unbelievable," he said when handed the microphone.
"I won today for you guys," he shouted, pointing into the crowd.
"This is a Philadelphia victory," he said before plunging into the crowd with the chrome trophy bearing the word Champion and topped with a leaping bass.
A Philadelphia victory is how it felt.
Every one of the 11 finalists who preceded Iaconelli to the weigh-in at the tournament - sponsored by Alabama's Bass Anglers Sportsman Society - had praised the Delaware River and its tributaries for the quality of its bass fishing. They said they had never encountered a tournament crowd like the one at Penn's Landing.
"The most fantastical fans I've ever seen in my life," said Kevin Short, who took third overall.
"There's never been a crowd like this," Shaw Grigsby told them to cheers, then turned to Mercer. "This wouldn't be a bad place to come back to," he told him.
"Philly fans are the loudest, most awesome I've found!" Skeet Reese shouted out.
Reese's fishing companion for the day had been former Phillies pitching star Roy Halladay, who said he met and first went wishing with Reese as a prize for his 2010 perfect game against the Florida Marlins.
Halladay took up the sport as a result of that first outing, "but I'll never fish like these guys," he told the delighted crowd.
The competition was the first time the Bassmaster Elite championship had been held on the Delaware, and it drew 106 of the nation's best bass fishers despite the river's reputation as an urban waterway famous for six-foot tides, three-knot currents, and lots of trash.
Competitors were eliminated each day until 12 were left for Sunday's final round.
Iaconelli told the crowd he had had to cast his lures in and around "drains, shopping carts, and barrels" to make his winning catches. "It was the nastiest stuff," he said to laughter.
His knowledge of the river currents and fishing holes helped explain his win, but luck and good instincts clearly played a role.
According to the tournament website, he made the catch that put him over the top about 1:55 p.m.
He had been heading downriver when "he suddenly made a 90-degree right turn and shut down."
"He pitched into a big metal crib around a retention pond drainpipe and flipped in a bass weighing close to two pounds," the website said, "and it made him a very happy man."