After a slowish start Leslie took the lead midway through the backstroke length and never looked like surrendering it.
Leslie said it was a battle but he was stoked with the effort.
"I certainly felt a mixture of a lot of pain out there tonight, but I just had to get through the motions and remember the process. It is so easy for the wheels to fall off, if you focus on the pain," he said.
"We [Cameron and coach Simon Mayne] set a very challenging target time coming into this competition and we knew if we hit that time a gold medal would be on.
"I am so glad we did set such a challenging one because Jin was pretty close behind in the end."
"I had no idea he was there, I was just focused on making sure I did the things I could control, right."
He pulled away during the breaststroke leg and despite a valiant finish from Jin, Leslie was too strong.
This is the third Paralympic Games in a row that Leslie has set the world record in this event, dominating since the Beijing 2008 Paralympic Games eight years ago.
Leslie was the first Kiwi in the pool this morning, setting a fastest time of 2:29.36 in the heats to qualify first.
In other Rio action, Liam Malone once again showed the sporting world that he meant business by setting a Paralympic record of 21.06secs in winning the men's 200m T44.
Malone showed his true power, moving through the race to cross the line ahead of USA's Hunter Woodhall (21.12) and German David Behre (21.41).
This adds to the silver medal he won in the 100m T44 on day two in Rio when he accelerated at a phenomenal pace through in the last 30m to take second.
Malone got his first set of blades following the support of the New Zealand public, who donated to a crowd-funding site to the tune of $20,000.
In yesterday's men's 200m T44 heat Malone cruised to the fastest qualifying time in 21.33sec, nearly two-tenths faster than Woodhall on 21.50 and two-tenths ahead of Behre. Malone appeared completely in control of the heat, checking his nearest rival twice on the way down the final straight and maintaining a small lead to cross in first.