Teenage swimmers Summer McIntosh and David Popovici lived up to their billing as future stars by winning gold medals in their respective events at the Paris Olympics on Monday.

McIntosh blitzed her rivals to win the women's 400m individual medley final in the opening medal race of the evening session at La Defense Arena.

Siobhan Bernadette Haughey of China's Hong Kong competes during the women's 200m freestyle final of swimming at the Paris 2024 Olympic Games in Paris, France, July 29, 2024. (Xinhua/Xue Yuge)

The Canadian led from start to finish to clinch gold in four minutes 27.71 seconds. Kelly Grimes of the United States took silver in 4:33.40 and her compatriot Emma Weyant claimed bronze in 4:34.93.

"I'm just trying to make team Canada proud and set the tone," McIntosh said. "I couldn't really see anything until the breaststroke, then I knew I was in a comfortable lead going into that last 100m. It was an amazing feeling."

The 17-year-old, who holds the world record in the event, said she was not overawed by performing on the Olympic stage.

"It's always just about having fun, as well as pushing my body to its limits," she said of her maiden Olympic title. "I try to take every event individually, one by one. I try not to get too high or too low."

Popovici also secured his first Olympic gold medal by winning the men's 200m freestyle final. The 19-year-old, already a dual world champion, touched the wall in one minute 44.72 seconds, just two hundredths of a second ahead of Britain's Matthew Richards.

Luke Hobson of the United States took bronze in 1:44.79.

Germany's Lukas Martens, who won gold in the men's 400m freestyle on Saturday, led early before fading in the final 50m to finish sixth.

"I feel amazing," Popovic said. "It's so great to be here. There are many Romanians in the crowd. It's beautiful, it's a dream come true. I don't know how to describe it. It's so simple, yet so beautiful."

Popovici has been touted as a future star since winning gold in the 100m freestyle and 200m freestyle at the world championships in Budapest two years ago.

On a night in which five gold medals were decided, South Africa's Tatjana Smith made a late surge to win the women's 100m breaststroke final.

Smith, the silver medalist in the event at the Tokyo 2020 Games, overtook China's Tang Qianting in the final 10 meters to touch the wall in one minute 5.28 seconds. Tang claimed the silver medal in 1:05.54 and Ireland's Mona McSharry took bronze in 1:05.59.

"I am going to keep my phone off," 27-year-old Smith said. "I don't know, I think everyone is so proud. Obviously I think they would have been proud even if I did not win a medal. That's what I am really grateful for, really just the people in my life, they have been so supportive."

Italian Thomas Ceccon secured Italy's second swimming gold medal at these Games by winning the men's 100m backstroke final.

Ceccon finished in 52.0 seconds, more than three tenths of a second faster than second-placed Xu Jiayu of China. Veteran Ryan Murphy of the United States took bronze in 52.39.

"I was emotional," Ceccon said. "This is very weird for me. I was even getting emotional before the race, because these are really strong emotions. Being in an Olympic final is not something everyone can say. It's a privilege."

In Monday's final race, Mollie O'Callaghan earned Australia's third gold in the pool at these Games by powering to victory in the women's 200m freestyle final.

O'Callaghan finished in an Olympic record time of one minute 53.27 seconds, more than half a second faster than her compatriot and defending champion Ariarne Titmus, who took silver.

Hong Kong China's Siobhan Haughey, a silver medalist in this event at the Tokyo 2020 Games, claimed bronze in 1:54.55.

"My expectations are very high. That was an amazing race. I'm always wanting that little bit more," O'Callaghan said. "I just had to go with coach Dean Boxall and trust him knowing what to do and what's best."