TOKYO — It happens so fast. After years of preparation, Lakeville's Regan Smith and her rivals walk to the pool, discard their robes and flip-flops, and dump them into a laundry basket set there by workers as a low-tech, moveable locker.

The swimmers quickly stretch or leap, or slap their thighs to awaken their muscles, then approach the edge of the pool.

On Monday morning in Tokyo, Smith was racing in the 100-meter backstroke semifinals, so she leaped into the pool, took her starting position and then arched back into the water.

She won the first heat in an Olympic record 57.86 seconds. For the second straight day she had set the record. This time, she held onto it, taking the record into Tuesday's final.

"It was great," Smith said. "I'm really pleased with it. I was just trying to clean some things up from last night and get ready for tomorrow. So I'll definitely take that. I'm really happy with it."

The Olympic and perhaps world record is likely to be broken in the final.

"Ultimately, it doesn't matter," Smith said. "Tomorrow is what I'm really shooting for. But, yeah, I feel great and hopefully I can just keep the ball rolling and keep the energy flowing into tomorrow."

It happens so fast. On Sunday night, Canadian Kylie Masse, in the fourth heat of the prelims, had set an Olympic record in the 100-meter backstroke at the Tokyo Aquatic Center.

"Having the record was amazing," the Canadian said. "I was happy to have achieved that, for one or two minutes."

She meant that literally.

In the fifth heat, Smith broke Masse's record. In the sixth heat, Australia's Kaylee McKeown broke Smith's record.

"I would be lying if I said I wasn't nervous," McKeown said.

The three record-breaking times: 58.17, 57.96 and 57.45.

Tuesday, Smith will try for her first Olympic medal. Strangely, she feels less pressure in Tokyo than she did at the U.S. Olympic trials.

"I was just saying how different this meet is,'' she said. "The environment is a lot easier to think and have a clear mind-set and be able to execute. I'm feeling good here.

"It will be a super fun race. There are so many talented girls. It will be very fun to watch, and I think it will be fun to be a part of, too.''

Before arriving in Tokyo, Smith and McKeown have been distant rivals and virtual friends. Smith set the world record of 57.57 at the World Championships in 2019. In June of 2021, McKeown swam a 57.45 to pass it.

That remains the record, but the finals in Tokyo promises to put that number in jeopardy.

Smith texted McKeown in May, when McKeown was competing in Australia. McKeown praised Smith for her sportsmanship.

Now the friendly rivalry will culminate on Tuesday morning in Japan in the final.

The three women who successively broke the 100-meter backstroke Olympic record on Sunday night all have held the world record.

"It's great competition,'' Masse said.