Kyle Chalmers, Dmitriy Balandin and Mireia Belmonte Garcia all claimed notable victories in the pool, while Katie Ledecky struck gold again.
Australian teenager Kyle Chalmers stole the show at the Olympic Aquatics Stadium on Wednesday, as the peerless Katie Ledecky claimed her third gold of Rio 2016.
Chalmers produced a stunning finish to triumph in the men's 100m freestyle final with a time of 47.58 seconds, having been seventh at the halfway stage.
The 18-year-old finished more than two tenths of a second clear of silver medallist Pieter Timmers, while Nathan Adrian - the champion in London four years ago - had to settle for third.
Ledecky anchored the United States team to a dominant victory in the 4x200m freestyle relay, while Michael Phelps and Ryan Lochte predictably eased into the final of the men's 200m individual medley, which takes place on Thursday.
Kazakhstan's Dmitriy Balandin was a shock winner of the men's 200m breaststroke final from lane eight, after recording the slowest qualifying time on Tuesday.
Mireia Belmonte Garcia earned Spain a first gold medal in women's swimming, edging out Australia's Madeline Groves by 0.03secs to take the 200m butterfly title.
RACE OF THE DAY
Japan's Yasuhiro Koseki appeared set to shatter the men's 200m breaststroke world record in Wednesday's first final. However, after setting a blistering pace, the Japanese faded badly in the closing stages as Balandin - the slowest qualifier - came on strong to take gold ahead of Josh Prenot and Anton Chupkov.
World record holder Cate Campbell twice lowered the Olympic record in the women's 100m freestyle on Wednesday, posting a time of 52.71 in her semi-final after clocking 52.78 in the heats. Campbell's sister Bronte also qualified for the final, along with the likes of Canadian teenager Penny Oleksiak, Simone Manuel, Sarah Sjostrom and reigning champion Ranomi Kromowidjojo.
QUOTES OF THE DAY
"I'm someone who does not follow swimming too much. I follow basketball, football and soccer," - the relaxed Chalmers reveals he is no swimming buff.
"It's my last Olympics and then I say farewell. It's a good way to say goodbye," - Timmers, the runner-up to Chalmers, says he will not be competing at Tokyo 2020.
"I think the whole of Kazakhstan will be drinking tonight," - 200m breaststroke champion Balandin expects his compatriots to rejoice in his success.
"I use hypnosis in my preparation. Did it work today? No, as you can see," Marco Koch tells it as it is after finishing seventh in the final Balandin triumphed in.
Phelps and Lochte's duel for the 200m IM title will top the bill on Thursday, while Cate Campbell will seek to maintain her fine form in the women's 100m freestyle final.