Russia retained the synchronised swimming duet free title as Natalia Ishchenko and Svetlana Romashina won gold at the World Championships on Friday.

The Russians scored 98.333 points to edge perennial bridesmaids Gemma Mengual and Andrea Fuentes of Spain into second by just half a point with Chinese twins Jiang Tingting and Jiang Wenwen taking home the bronze.

Russia, who dominate synchronised swimming, were the reigning champions although with previous pairing Anastasia Davydova and Anastasia Ermakova.

For Ishchenko this was her third gold medal at these championships and her ninth world title, while it was Romashina's second gold here in Rome.

Romashina partnered Davydova to duet technical gold earlier in the week while Ishchenko won both the solo free and solo technical competitions.

"We are very happy to have secured the gold medal. We wanted to distinguish ourselves from the other swimmers," said Romashina.

"Our performance was perfect, our choreography was easy and full of little details."

Spain's Mengual finished second to Russians in all those events and now has 10 silver medals from world championships as well as seven bronze.

But at the age of 32 she finally broke her gold medal duck on Wednesday when Spain won the free combination team event.

But having criticised the judging in Thursday's solo free event, Mengual admitted they had been beaten by the better pairing this time.

"I believe this time we have been evaluated correctly and the final score reflects the level of our performance," she said.

Meanwhile, Jiang Wenwen revealed just why the Chinese have improved so dramatically over the last year.

"There are moves that only we as twins can perform," she said. "This is also because our legs are as long as each other's."