Barcelona, Spain ? One world record inspired Michael Phelps to go for more.

The 18-year-old American set world records Friday in the 100-meter butterfly and 200-meter individual medley at the World Swimming Championships and became the first man to break world records in two individual events on the same day.

In all, nine world marks have been broken and one equaled at these championships, which end Sunday.

The 100 butterfly record gave Phelps a world mark in his fourth discipline. No other current male or female swimmer holds four individual records.

“I’m excited for sure,” said Phelps, of Baltimore. “After the 100 fly world record, I was very fired up. Coming into the second one, I wanted to break it again. So I just went out there and laid it on the line in the first 100 and tried to hang on.”

Phelps broke the butterfly record during the semifinals and topped the mark set by Andrii Serdinov of Ukraine five minutes earlier. Phelps’ time was 51.47 seconds. The previous record, set by Serdinov in the previous semifinal, was 51.76. Serdinov’s time beat the mark of 51.81, set by Michael Klim of Australia Dec. 12, 1999, in Canberra, Australia.

Forty-five minutes later, Phelps broke his own world record in winning the gold in the 200 IM. Twenty-four hours earlier he swam 1:57.52 in the semifinal heat to set a world record. That replaced the world record of 1:57.94 he set last month in Santa Clara, Calif.

Tuesday, he broke his own world record in the 200 butterfly with a time of 1:53.93. His previous mark of 1:54.58 was set July 24, 2001, in Fukuoka, Japan.

He also holds the 400 individual medley world record (4:10.73). The 400 IM semifinals and finals are Sunday.

Michael Phelps kisses his 200-meter individual medley medal after becoming the first man ever to set two world records on the same day. Phelps' made history Friday at the World Swimming Championships in Barcelona, Spain.

Serdinov started the record frenzy in the 100-meter butterfly semifinals, only to be topped by Phelps in the second heat.

“That first world record fired me up big time,” Phelps said. “When (Serdinov) hit the wall I was pumped.”

In the next event, Phelps’ fellow American Amanda Beard tied a world record when she won the gold in the 200 breaststroke.

Australia’s Ian Thorpe, who is being challenged by Phelps for the title of world’s best swimmer, took the silver medal in the 200 IM in 1:59.66, more than 3.5 seconds behind, an eternity in this event. Italy’s Massimiliano Rosolino (1:59.71) won the bronze.

Phelps’ records read like this: 200 IM, 1:56.04; 100 butterfly, 51.47; 200 butterfly, 1:53.93; and 400 IM, 4:11.09.

Phelps, who became the youngest man to break a world mark when he was 15, has a chance match Mark Spitz’s seven Olympic gold medals next year in Athens as he bids for gold in four individual events and three relays.

Beard won the 200 breaststroke in 2:22.99, the same world mark China’s Qi Hui established two years ago. Australia’s Leisel Jones took the silver medal in 2:24.33 and Qi claimed the bronze in 2:25.78.

Another American, Aaron Peirsol, won the gold in the 200 backstroke in 1:55.92, ahead of silver medalist Gordan Kozulj of Croatia (1:57.47) and bronze medalist Simon Dufour of France (1:57.90).

Hanna-Maria Seppala became the first Finnish woman to win a gold medal at the worlds by taking the 100 freestyle. Seppala finished in 54.37, ahead of Jodie Henry (54.58) and bronze medalist and eight-time Olympic champion Jenny Thompson of the United States (54.65).

Grant Hackett of Australia won the 800 freestyle gold in 7:43.82. Larsen Jensen of the United States took the silver in 7:48.09 and Ihor Chervynskyi of Ukraine earned the bronze in 7:53.15.

Four-time Olympic champion Alexander Popov of Russia posted the fastest time (21.99) in the 50 freestyle semifinals. Popov, who holds the world record of 21.64 in the 50 free, also swam under 22 seconds in Friday morning’s qualifying. Thursday, Popov won the 100 free.

Jason Lezak of the United States was second fastest in 22.14, followed by Johan Kenkhuis of the Netherlands in 22.31.

In the women’s 50 butterfly semifinals, Dutch sprinter Inge De Bruijn led in 25.94, ahead of China’s Zhou Yafei and Sweden’s Anna-Karin Kammerling. Stanislava Komarova of Russia led the women’s 200 backstroke semifinals in 2:09.39.