Already with a 4x100-metre freestyle relay gold, McKeon is a genuine shot in the 100m butterfly final.

While China's Yufei Zhang was quickest into the medal race, McKeon wasn't far behind - and that swim came in a session when she also picked up relay gold.

McKeon is a contender for seven medals in Tokyo, which would be the most of any Australian at a single Olympics.

Australia enter Monday's competition with one gold, one silver and one bronze - all swimming.

But McKeon and fellow swimmer Ariarne Titmus are set to add to that collection on day three at the pool.

The 20-year-old Titmus, in the 400m freestyle final, takes on American megastar Katie Ledecky, the world's best-ever female swimmer.

Australia's men's 4x100m freestyle relay team are eyeing a medal but appear off the gold pace set by Italy and the United States.

Elsewhere in the Olympic city, world No.1 tennis star Ash Barty, who suffered a stunning opening-round singles loss on Sunday, must regroup for the doubles.

Barty and Storm Sanders play China's Yifan Xu and Zhaoxuan Yang in a second-round fixture.

The Hockeyroos also play China after starting their campaign with a win over Spain.

Likewise, the Stingers will aim to build on a first-up win against Canada when they take on the Netherlands in women's water polo.

Australia's softballers face their moment of truth: they must beat Mexico to reach the bronze medal game. while in women's skateboarding Australia's world No.6 Hayley Wilson is an outside medal chance.

Paul Adams is well-placed in the skeet, with two more preliminary rounds on Monday before the top six contest the medals, while Laura Coles is further back in the women's field.

Dan McConnell will contest the cross-country mountain bike event at his fourth Olympics, the day before his wife Bec starts the women's race as a medal contender.

Jake Birtwhistle is the main Australian medal hope in the men's triathlon, with Aaron Royle and Matt Hauser likely to work for him.

Jian Fang Lay takes on Poland's Qian Li, while David Powell plays Slovakian Yang Wang in the second round of the table tennis singles draws.

Daniel Watkins is in the semi-finals of the canoe slalom, with the medals to be decided on Monday, and Australian surfers Stephanie Gilmore, Sally Fitzgibbons, Julian Wilson and Owen Wright are scheduled for round-three heats.

Australian Associated Press