The Canadian won the women's 100 metres butterfly - the event she was crowned champion in at Tokyo 2020 - at the Aquatic Center Laguna Los Morros.

MacNeil's time of 56.94sec broke a Games record which had stood since Toronto 2015.

The second medal of the session for MacNeil then arrived in the mixed 4x100m freestyle relay as Canada took bronze.

Brazil won gold in 3min 23.78sec, a Games record, with the US taking silver.

"I was wearing my goggles when I saw that I broke the record, and when I took them off, I couldn't believe it," said MacNeil.

"It’s always tough doing a double with a quick turnaround, and it's just about trying to recover and prepare for the next one. 

"It's always easier to get ready for a relay because you know everyone else will pull you out after a good or bad swim."

MacNeil had already won gold in the 4x100m freestyle relay on the first day of swimming at Santiago 2023. 

The US starred on day two with four golds, including Jack Aikins taking home the men's 200m backstroke title in a Games record 1:56.58.

Kennedy Noble was another American to clock a Games record as she won the women's 200m backstroke in 2:08.03.

In the men's 200m freestyle, Coby Carrozza of the US came home to win in 1:47.37 and his team-mate Lukas Miller was the men's 100m butterfly champion in 51.98.

Canada added another gold as Mary-Sophie Harvey won the women's 200m freestyle in 1:58.08.

In diving, Mexico and Canada won gold medals at the Aquatics Centre.

Mexican world bronze medallists Kevin Berlín and Randal Willars won the men's 10m platform synchro final with a score of 419.94 points and the women's 1m springboard gold went to Canada's Pamela Ware on 280.25.

Two athletics golds were decided as the men's and women's marathons were held in the morning.

Peru's Cristhian Pacheco won the men's race in 2 hours 11min 14sec as he finished alone at the end of the field, defending the title he claimed at Lima 2019.

His time was nearly two minutes behind the 2:09:31 he had run to win in Lima four years ago when he set a Games record. 

"I had an accident four weeks ago," said Pacheco. 

"At that time, I wasn't certain about making a quick recovery, but with dedicated therapy and the invaluable support of my coach, we prepared to ensure I would be performing at peak condition for the Pan American Games."

Mexico's Citlali Cristian broke the previous Pan American Games record by more than three minutes as she won the gold medal in the women's marathon in 2:27:12.

It was the fourth consecutive edition of the Pan American Games that the event's record had been broken in the women's marathon, including at Lima 2019 when Peru's Gladys Tejeda had won in 2:30:55.

Double Olympic gold medallist Mariana Pajón won her third Pan American Games title in the women's BMX for Colombia as Kamren Larsen of the US took home the men's title at Circuito.

In road cycling, Kristen Faulkner of the US won the women's time trial in 25:45, completing a fine comeback after she fractured her knee in June after being hit by a car.

Walter Vargas of Colombia won the men's time trial in 47.02.

In skateboarding at the Urban sports Esplanade, Taylor Nye of the US dominated the men's park competition to win on 86.6 as 13-year-old Fay Ebert took the women's title for Canada on 84.66.

The men's speed title in sport climbing went to American Sam Watson at Cerrillos Park, who stopped the clock at 5.37 in the final against team-mate Noah Bratschi.

Mexico enjoyed a good day at the taekwondo with two golds at Contact Sports Center, including the women's under-67 kilograms title for former world champion Leslie Soltero.

William Arroyo added his second gold of the Games as he took the mixed poomsae pairs crown with Soo Lee Kim.

Canada's Skylar Park won the women's under-57kg title and the men's under-80kg gold went to American Carl Nickolas.

In the women's 59kg weightlifting at Gimnasio Chimkowe, Yenny Álvarez won gold for Colombia on 228kg, a Games record.

The men's 89kg title went to Keydomar Vallenilla of Venezuela and Angie Palacios of Ecuador topped the podium in the women's 71kg.