GWANGJU, SOUTH KOREA – American swimmer Caeleb Dressel answered most of his critics about his readiness to defend his seven world swim titles with a course record and American record semifinal split in Sunday’s first event of the week long FINA Swimming World Championships, then, to double down, winning the Monday final with a newer American record for his first individual gold medal.

In the 50 butterfly in Sunday’s semifinal, Dressel cranked out a 22.57 American record to take the top time going into the final, then crashed the field with an even-better 22.35 split to win gold over Russia’s Oleg Kostin at 22.70. Brazil’s Nicholas Santos took bronze in 22.79. The gold medal was the first time an American won gold in the world 50 butterfly.

“Good, better, best,” said Dressel, in a post 50 fly interview on NBCSports. “Coach Troy said just keeping improving throughout the meet. I was a little anxious this morning. Took a walk and just got rid of that funk. I’m really happy with the outcome. It didn’t come easy.”

At the 2017 world championships, Dressel finished a disappointing fourth in the final for his only non-medal winning event.

The world record, owned by Ukrania’s Andrii Govorov, who finished sixth in Monday’s final, is still at 22.27.

In the womens 400, American, and Olympic gold medalist and world record holder Katie Ledecky, three times the 400 meter world champion and a 15-time world champion for distance swimming, was stunned in the final 50 meters by Australian Ariarne Titmus, 19, who won in 3:58.76 with Ledecky nearly a second off the pace in second place in 3:59.97.

Dressel, 22, and a graduate of Clay High School where he won numerous state titles, blasted the star studded field with his 22.57 second time in the 50 butterfly semifinals. Dressel’s previous American record was 22.76 set at the 2017 World Championships as the top qualifier in the semifinals and was Dressel’s only event that he did not medal finishing fourth in 22.89.

Ukranian butterfly specialist Andriy Govorov, the world record holder at 22.27, won the first semifinal heat in 22.80.

Dressel, who has been struggling since turning into a professional swimmer after dominating the NCAA swim championships for four years while at the University of Florida, roughed up the field in the semifinal heats with Brazil’s Nicholas Santos, the runnerup at the 2017 FINA World Championships, second at 22.77 and Oleg Kostin of Russia third at 22.88.

In the final, American Michael Andrew, who defeated Dressel twice in the USA Nationals earlier in the year, was fourth in 22.80 with defending world champion Ben Proud of Great Britain seventh at 23.01. Govorov was sixth at 22.91.

Also, in the 4 x 100 freestyle, Dressel and the American team set a record of 3:09:06 to take gold. Dressel led off at 22.74 with Italy and two other swimmers ahead of world record pace for the 100 free. Dressel would finish off the world record with a 47.63 leadoff with Blake Pieroni, Zach Apple and Nathan Adrian joining him for the gold medal. Russia was second at 3:09.97.