It was a counter left hook against the charging Whittaker that did the damage, and the following hammerfists gave the referee no choice but to stop the fight.
"It was probaly one of my toughest tests but I made it look easy," Adesanya said.
"It's crazy. Sometimes I have to pinch myself and say 'man, did that just happen'.
"I knew he was going to start fast and fall over himself. Like my coach said, what makes him dangerous makes him vulnerable."
It caps off a rapid rise for Adesanya, who made his debut with the UFC in February last year. It was his third knockout in seven UFC bouts, with all other wins coming from the judges' scorecards.
"I showed I can take it but I can give it as well - but apparently I don't have knockout power and have pillow hands," Adesanya said.
"I'm still all hype, by the way. I'm just a hype train."
Adesanya said he thought the fight was over for a split second when he dropped Whittaker at the end of the first round, before realising the referee interferred because the round was over.
Headlining the most well-attended card in UFC history, with more than 57,000 in the stadium, it was a different story to when the UFC held an event at the same venue in 2015, when Adesanya was simply another face in the crowd.
"I was in the nosebleeds, and now I made his nose bleed," he said in the octagon after the fight.
The win finished off a trifecta of victories for the City Kickboxing stable, with Dan Hooker beating Al Iaquinta and Brad Riddell beating Jamie Mullarkey - both by unanimous decision.
The Kiwi contingent won three of four fights on the card, with Hamilton's Luke Jumeau losing in a split decision against Brazilian Dhiego Lima.
Adesanya was awarded a US$50,000 performance of the night bonus, alongside Cape Verde's Yorgan de Castro, who took a knockout win over Justin Tafa, while Riddell and Mullarkey also earned bonuses for fight of the night.