The 20-year-old swam the second fastest time in history to claim gold, the Wollongong star finishing second.

Read more: Dragons hit fresh low with heavy Bulldogs defeat

The swim secured McKeon her second individual swim at the Games, along with the 100m butterfly.

Titmus swam into the record books, her time of 1:53.09 the fastest since Frederica Pellegrini swam 1:52.98 in a supersuit in 2009.

The Tasmanian was patient throughout the first 100m before swimming over the top of McKeon in the second half of the race.

"No one's really been close to beating [the record] in a long time," Titmus said. "Tonight I knew if I swam the way I wanted to race I had a 1:53 in me.

"I was pretty nervous, but last night's swim definitely gave me the confidence."

With McKeon and Titmus leading the way, the Australians have raced into gold-medal contention for the 4x200m relay.

Madison Wilson and Leah Neale rounded out the top four, the team looking to build on the 2016 silver.

McKeon's swim was another consistent performance for the 27-year-old and she's already identified areas to improve in Tokyo.

"My front end's always a strength of mine in the 200," McKeon said. "To swim a good 200 you have to put your body on the line, so I feel like I did that.

"When I swim a 200 I always know as soon as I touch the wall where I can improve for next time, but I gave it everything I had tonight."