Michael Andrew crashed through the 51-second barrier to win the 100m butterfly at the Indianapolis Pro Swim Series in 50.80sec on Friday, one month before the US Olympic swimming trials.
Andrew, coming off an impressive win in the 100m breaststroke on Thursday, had lowered his personal best to 51.31 in the 100m fly heats.
The 22-year-old then set a Pro Swim Series record in the final with the second-fastest time in the world this season behind the 50.47 posted by Hungarian Kristof Milak.
"It was pretty much exactly what I planned on doing this evening," Andrew said. "I would have liked to go 50.5, but the race execution was great.
"I knew that this morning I finished really well, so this evening I just wanted to put in as much speed as I could going out, and I think I was to the wall in 23.3 and then I closed nicely.
"I feel like this whole weekend is just building confidence going into trials."
Caeleb Dressel, the world record-holder and two-time defending world champion, was putting in his trials preparation at the Atlanta Classic meeting on Friday, where he won the men's 100m fly in 51.15.
Dressel overtook Tom Shields on the second lap, Shields capturing second in 51.55.
Back in Indianapolis, collegiate champion Phoebe Bacon clocked 2min 06.84sec to beat world record-holder Regan Smith in the women's 200m backstroke.
Bacon seized a narrow lead on the penultimate lap and held on -- both swimmers clocking the same split for the final length that left Smith in second in 2:96.90.
"I knew both of us were going to be out fast, and I knew I could keep up with her on that first 100," Bacon said. "For me, it was just all about hammering down that last 100, especially that last 50. I knew I couldn't let her get out of my eyesight."
Smith came back later to win the women's 100m butterfly in 57.68, with Kelsi Dahlia second in 57.75.
"I was hoping to pull something a little faster here, but I'll take it," Smith said. "It was a tough double tonight and it was a great race, we were all right on top of each other so to come out with the win is great."