The first session in the Olympic Aquatics Stadium saw the first swimming world record broken as Team GB’s Adam Peaty lowered his own 100m breaststroke mark by nearly half a second.
The world, Commonwealth and European champion dominated heat six, winning by well over a second from Australia’s Jake Packard.
Fellow Brit Ross Murdoch also qualified for Saturday night’s semi-finals, where Peaty hopes to improve his new world record time of 57.55 seconds even further.
“I just raced today and did what I had to do. I’ve become an Olympian now and that’s a good thing," he said.
“Hopefully tonight I’m going to move the record on even more and see what I’ve got. Hopefully tonight I’ll feel a lot better and will be able to swim faster.
“I’m not going to get too complacent now. I’m going to keep striving, keep pushing the boundaries and see what I get.”
Peaty’s new record sits just shy of a second faster than Cameron van der Burgh’s old mark, which the Uttoxeter swimmer surpassed in April 2015.
The 21-year-old’s swim topped off a successful afternoon in the pool for British swimmers.
Max Litchfield got the ball rolling in the day’s first event, qualifying for the final of the 400m individual medley, while James Guy qualified for the 400m freestyle final as Stephen Milne smashed his personal best in the same heat.
Another Games debutant Aimee Wilmott qualified alongside three-time Olympian Hannah Miley for the women’s 400m individual medley final on Saturday night.
“We’ve not mentioned medals in the team. For us it’s making sure we do a season’s best and for everybody to reach their own individual goals,” Miley said.
“The atmosphere is really calm and it’s been a wonderful team to be a part of. Two thirds of the team are first-time Olympians so there’s a lot of new energy and excitement. Team GB is in a good place.”