“I love this pool, I knew I put in the work to have a good swim and got into a rhythm,” Ledecky said.
“I’ve got the relay, that’s next on the agenda and then I will tackle the 800m. We’ll see (if I can get a record).”
Ceccon, 21, finished the 100m backstroke with a phenomenal time of 51.60 seconds — 0.25 seconds better than American Ryan Murphy’s previous mark.
Murphy, a four-times Olympic gold medallist, finished second while fellow American Hunter Armstrong was third.
“I have no words, there was an Olympic champion in 2016 (Murphy) and other strong people (in the field). I’m pretty happy,” said a speechless Ceccon.
Earlier, Romanian teenager David Popovici smashed the world junior record as he powered to victory to take gold in the men’s 200 metres freestyle event.
The 17-year-old became the first male Romanian swimmer to win gold at the world championships as he finished with a time of 1:43.21.
He finished more than a second ahead of South Korea’s Hwang Sun-woo while Britain’s reigning Olympic champion Tom Dean finished third.