After beating teammate Ariarne Titmus in the women's 200m freestyle final on Monday, 20-year-old O'Callaghan was unable to repeat her strong performance and finished fourth on Wednesday night.

Sweden's Sarah Sjoestroem won in 52.16 seconds, USA's Torrie Huske (52.29) took silver and Hong Kong's Siobhan Bernadette Haughey won bronze.

There were more tears on Monday night in Paris. Only they were tears of happiness, jubilation and relief. O'Callaghan may have lost the battle last month, but in the packed La Défense stadium he won the war. In one of the most anticipated bouts of the meet, O'Callaghan got his revenge and won his first individual Olympic gold in a frantic four-round battle with Titmus. It is the first time in 20 years that two Australian swimmers have won an Olympic gold medal, following in the footsteps of Ian Thorpe and Grant Hackett.

I was very nervous," O'Callaghan said. "I haven't slept much in the last few days and I've been trying very hard to control myself and get up. 

– I knew the 100m freestyle was going to be difficult because it relies a lot on speed and that's something I lack.

In the semifinals of the women's 100m backstroke, Australia's Kaylee McKeown qualified second ahead of Tuesday night's medal race. The 23-year-old Australian is the reigning Olympic champion in the 100m and 200m backstroke, and in Paris she will also compete in the 200m individual medley. She is likely to take three gold medals.

O'Callaghan beat teammate Ariarne Titmus for the gold medal in the 200-meter freestyle and was also part of Australia's victorious 4x100-meter freestyle relay team at the Paris pool.