BUENOS AIRES (Reuters) - Switzerland's Sebastien Buemi became the first driver to win three Formula E rounds in a row on Saturday with Argentine fans also witnessing another milestone with a 'race' between two driverless cars on the streets of Buenos Aires.

Buemi, the reigning champion and an ex-Formula One driver, has now won all three races this season for the Renault e.dams team with Buenos Aires following on from Hong Kong and Morocco.

He leads the standings by 29 points from Brazilian Lucas Di Grassi with the next race in Mexico City on April 1.

Renault e.dams have now won half of all the Formula E races that have taken place.

Frenchman Jean-Eric Vergne was second in Saturday's race for the Chinese Techeetah team with Di Grassi, who started on pole position, third for Team Abt Schaeffler Audi Sport.

Buenos Aires also saw the first demonstration run of two driverless 'Roborace' development, or 'DevBot', electric cars running on track together at speeds of up to 185kph but mostly slower.

The cars used sensors and on-board systems to navigate the street circuit whilst communicating with each other to avoid contact but one of the two still crashed into barriers.

A stray dog on the track posed an additional hazard.

"This is an historic moment for Roborace and for the future of autonomous vehicle development," said Roborace chief executive Denis Sverdlov in a statement.

"Seeing these two cars interacting at speed on a race track shows how fast the technology is progressing and how important a platform Roborace is for further development.

"It is so exciting to see these vehicles functioning without any human intervention, making their own decisions and taking appropriate actions in order to guide themselves around the track."

Formula E organizers hope ultimately to have up to 10 driverless cars racing together, run by teams who write their own software, around city tracks as a support event to their series.

(Reporting by Alan Baldwin in London, editing by Toby Davis)