Kate Douglass underlined her remarkable versatility with gold in the women's 200 metres breaststroke at the Paris Olympics on Thursday, beating Tokyo champion Tatjana Smith who bows out of a stellar swimming career with a silver medal in her final race.

Taking full advantage of her turning prowess, American Douglass nudged ahead of Smith after every length and held off the South African to touch the wall in 2:19.24 at La Defense Arena.

"I'm really excited. I feel like for a while I wasn't sure if Olympic champion was going to be possible for me to say, and now it's just really exciting to see it happen," Douglas told reporters.

World champion Tes Schouten won bronze for the Netherlands, her first Olympic medal.

In the men's finals, Hubert Kos took Hungary's first swimming gold of the Paris Olympics when he won the men's 200 metres backstroke.

Greece's Apostolos Christou took the silver and Switzerland's Roman Mityukov the bronze.

Australia rounded out the evening with victory in the women's 4x200 metres relay.

The world record holders didn't have it all their own way though, as they were pushed hard in the first three legs by the US and defending champions China.

In the end, world record holder Ariarne Titmus anchored the Aussies to an Olympic-record winning gold while the US took silver and China the bronze.

The US silver meant also that Katie Ledecky became the most decorated female swimmer of all time with 13 Olympic medals. (Agencies)