Russia won three titles on their golden Friday at the world championships as the controversial Yuliya Efimova won the women's 200m breaststroke title to gain revenge over arch-rival Lilly King.
Russia also won gold in the men's 200m breaststroke final, plus the men's 200m backstroke and a silver in the men's 4x200m freestyle relay, but the real drama was Efimova's breaststroke victory.
The Russian clocked two minutes, 19.64 seconds after a powerful last 50 metres, finishing 2.13 ahead of second-placed Bethany Galat, while America's King, who led after the first length from lane eight, faded to finish fourth at 2.47 back.
It was a clear defeat for King, the 100m Olympic champion, who sparked a war-of-words with the Russian at the Rio de Janeiro Games last year after labelling Efimova a "drug cheat" due to her 16-month ban for doping up until February 2015.
Frictions between the pair have bubbled since.
On Tuesday, King broke the world-record in winning the women's 100m breaststroke gold, when Efimova finished third and the Russian relished victory over the longer distance.
"Lilly King congratulated me, I didn't see her during the race, as she was in lane eight, but she was on my mind throughout," admitted Efimova, who avoided the post-final press conference as she is racing again on Saturday.
Silver medallist Galat was impressed with Efimova's powerful display.
'Heck of a swimmer'
"I don't know Yuliya personally, her time was incredible -- she's a heck of a swimmer and a heck of a breaststroker," said America's Galat.
In the wake of Efimova's win, Anton Chupkov took the men's 200m breaststroke final to complete the double, by clocking a new championships record of two minutes, 06.96 seconds, and the 20-year-old hailed Russia's success.
"Finally, this has happened. Our national team did very well today, the best day for Russia so far -- three golds and one silvers reflects our improvement," said Chupkov.
"There were two golds before me, I heard the anthem and it was inspiring."
Russia's hat-trick was started by Evgeny Rylov in the men's 200m backstroke title.
Rylov, 20, clocked one minute, 53.61 seconds to take gold with Olympic 100m and 200m champion Ryan Murphy of the United States second at 0.60.
Murphy paid his dues to the new world champion and the American said he will have to train hard just to match him.
"I'm definitely disappointed, I'm a competitor I want to be the guy that's finishing first," said Murphy, who also had to settle for bronze over 100m.
"That has the best time in the world, so yes, it definitely stings."
Gold for Manuel
The Americans did have something to cheer as Simone Manuel won the women's 100m freestyle final to leave Sweden's Sarah Sjostorm, who broke the world-record holder on Sunday, to settle for silver.
Manuel touched the wall at 52.27 seconds with Sjostrom at 0.04 back while Pernille Blume of Denmark took bronze at 0.42.
"It's sad when I can't do it," said Sjostrom.
"I went out fast, it felt really good in the first 50m, but I'm totally destroyed -- now there's so much pain in my muscles."
There was little joy for Australia in the final as defending champion Bronte Campbell was seventh at 0.91 while compatriot Emma McKeon was last at 0.94.
Great Britain finished the night with gold in the men's 4x200m freestyle relay as James Guy sealed victory with a powerful anchor leg as Russia took silver and the USA third.