British teammates, Tom Dean and Duncan Scott, took gold and silver in the men’s 200m freestyle.
It is the first time since 1908 that two male British swimmers have finished on the Olympic podium together.
In a fast, closely-fought final, Dean touched home just ahead of world number one Scott on his debut Games.
Scott finished just 0.04secs behind his team-mate, with Fernando Scheffer of Brazil taking bronze.
Scott, who qualified fastest, was the favourite going into the race but Dean was able to back up his rapid start with a strong finish.
Scott said: “A massive credit to Dean. That was unbelievable. Olympic champion. He’s come along so far in the last 18 months, it’s a pleasure to watch. It’s great to be able to say he’s a good mate out of the pool and it’s great to be able to compete against him as well.”
Dean said: “I knew it was going to be a dogfight. I didn’t know how people were going to swim it. I just want to say thanks to everyone back home. I’m just lost for words. It’s amazing.”
The performances make Great Britain favourites for the 4x200m freestyle relay later this week. Scott also has a strong chance in the 200m individual medley.