Watch: Australia makes case to dethrone U.S. as top swim nation after Day 4 in Paris

Now halfway through the Olympic swimming competition in Paris, the U.S.-Australia rivalry is beginning to show an early head-to-head leader.

While the Americans lead in total medals (AUS 8, USA 15), the Australians have won more golds (AUS 4, USA 2), which are valued higher in the Olympic medal table.

Tuesday offered the latest in event finals featuring Aussies and Americans in which the latter was out-touched for first by a swimmer from Down Under.

Team USA's Regan Smith and Katharine Berkhoff earned silver and bronze in a tight women's 100 backstroke final in which Australia's Emma McKeown made a late charge to win gold.

But to finish off Tuesday's session, Team USA topped the Australians for silver in the men's 4x200 freestyle relay. Great Britain claimed its second consecutive gold in the event over both countries.

Monday featured a dominant Australian finish in the women's 200 freestyle final as teammates Mollie O'Callaghan and Ariarne Titmus secured gold and silver, respectively. The only American to make the final finished eighth.

The fierce rivalry between both countries is decades old, but reached a new fever pitch ahead of the Paris Games when Australian swimmers began exchanging competitive barbs with American legend Michael Phelps.

With four more days to go in the swim program, the U.S. still has ample opportunity to keep its crown, but it will have its work cut out with a seemingly revamped Australian team.