Barcelona - Ryan Lochte, James Magnussen and Liu Zige on Thursday won the early gold medals on offer at the world swimming championships, while Rikke Moller Pedersen broke the women's 200m breaststroke world record.
Lochte won his first gold medal in the Palau Sant Jordi pool as he finished first in the 200m individual medley.
Lochte, who on Sunday won silver with the American 4x100m freestyle relay, won in 1:54.98, beating Japan's Kosuke Hagino by 1.31 seconds. Brazilian Thiago Pereira was just 0.01 seconds behind for the bronze.
In the men's 100m freestyle event, defending champion James Magnussen, who lost out on Olympic gold by 0.01 seconds, came from fifth at the turn to win in 47.71, beating Americans James Feigen (47.82) and Olympic champion Adrian Nathan.
Russian Vladimir Morozov, who was lying 0.23 under world record time at the split, faded after the turn and finished fifth - 0.30 behind the winner.
China's Liu Zige denied local favourite Mireia Belmonte gold in the women's 200m butterfly. The 2008 Olympic champion won in 2:04.59, with Belmonte taking silver 0.19 behind. The bronze went to Hungarian Katinka Hosszu.
Pedersen, 24, who led her semi-final in the women's 200m breaststroke from the start, finished in 2:19.11 seconds - 0.48 seconds faster than the old mark held by American Rebecca Soni.
Russian Yuliya Efimova had the second-fastest time, with local favourite Marina Garcia following.
It was the third world record at the 15th FINA world championships on the fourth day of competition.
Lithuanian Ruta Meilutyte was the first on Monday in the 100m breaststroke, followed by Katie Ledecky in the women's 1,500m freestyle final.
Both Meilutyte and Ledecky are only 16 years old.
In the women's 100m freestyle semi-finals, Sweden's Sarah Sjostrom topped the qualifiers into Friday's final in 52.87 seconds, followed by Malawi-born Cate Campbell, who lives and swims in Australia.
Ranomi Kromowidjojo and Feemke Heemskerk from the Netherlands had the third and fourth-fastest time.