GWANGJU, Korea, Republic Of -- Canadian swimmer Maggie MacNeil has won the country's first gold medal at the world aquatic championships.

The 19-year-old from London, Ont., competing on her first senior national team, stunned many observers by winning the women's 100-metre butterfly on Monday.

MacNeil set a Canadian record with a time of 55.83 seconds, 0.39 seconds ahead of reigning Olympic champ and world-record holder Sarah Sjostrom of Sweden.

Emma McKeon of Australia was third.

Canada now has one gold, two silver and two bronze medals at the two-week long event, featuring swimming, artistic swimming, diving and water polo.