Svetlana Kolesnichenko and Alexandra Patskevich underlined Russia's complete domination in sychronised swimming by adding the free duet crown to the technical title they had already claimed at the International Swimming Federation (FINA) World Championships in Budapest.
It marked Kolesnichenko's fourth gold medal of the week and marked Russia's fifth in six events.
The duo, who each formed part of the victorious Russian team at Rio 2016, proved too strong for their rivals at Varosliget Park.
They scored 97.0000 to comfortably defeat Chinese twins Jiang Tingting and Jiang Wenwen, who scored 95.3000.
“We worked hard to gain this result - 10-hours training almost every day at maximum limit," said Kolesnichenko.
"This was totally worth it.
“I’m so pleased to be the four-time world champion and the most titled synchro swimmer in Budapest.
"But I’m also happy, that the competitions are over for me.
"Now I’ll cheer up for the Russian free team and free mixed duet.”
Kolesnichenko has now taken free and technical solo and duet titles to take her career haul to 13 World Championship victories.
Ukraine’s Anna Voloshyna and Yelyzaveta Yakhno took bronze in in 93.2667.
France won the open water swimming 5 kilometres mixed team relay as the race took place using a new format.
Logan Fontaine, Aurelie Muller and Jeannie Maryse Oceane Cassignol gave the team the perfect platform before individual 5km winner Marc-Antoine Olivier completed the hob,
He finished 12.2sec clear of United States anchor Jordan Wilmovsky in 54min 5.9sec.
Each team consists of two men and two women racing in whatever order they prefer.
Italy took bronze on Lake Balaton, 25.1 seconds behind France.
Xie Siyi claimed the men's 3m springboard title in the last final of the day after his Chinese team-mate Cao Yuan missed two straight dives.
Xie scored 547.10 to finish comfortably clear of Olympic bronze medallist Patrick Hausding of Germany, who scored 526.15 for silver.
Ilic Zakharov took Russian bronze with 505.90.
Cao slumped to 10th, five places behind Britain's Olympic silver medallist Jack Laugher.