By Mary Milliken

RIO DE JANEIRO (Reuters) - First-time Olympian Zhang Mengxue secured China's first gold medal of the 2016 Olympics on Sunday by winning the women's 10-metre air pistol event and extending her nation's gold medal streak in the sport.

Coming off a tough qualifying round, the 25-year-old Zhang handily won the final with a score of 199.4 points in 20 shots, well ahead of 19-year-old Vitalina Batsarashkina from Russia, the silver medalist with a score of 197.1.

Anna Korakaki from Greece won the bronze, becoming the first Greek woman to win a medal in shooting.

Zhang kept China in top standing in the event after countrywoman and London 2012 and Beijing 2008 gold medalist Guo Wenjun failed to qualify for the finals, finishing in 30th place.

Zhang established her lead midway through the event and pulled away with a 10.9 perfect shot in the final rounds. Her score is an Olympic record under the new finals format.

Ranked fifth in the world, Zhang said she felt her only obligation was to qualify, but she barely made it, coming in seventh out of eight finalists.

"I was pretty calm for the final actually, because the qualification was a bit tough for me," said Zhang, who joined the national team two years ago.

By midday Sunday, China had six medals so far in the Rio Games, Zhang's gold, two silvers and three bronzes.

For Batsarashkina, who won her country's second medal of the Games, it was "not the best final, but it is the Olympic Games and somehow it happened."

She stressed that Russia's problem with dozens of athletes being banned from the Olympics for doping violations has nothing to do with her or other athletes.

"I don't think this is an athletes' problem, this is an issue of the countries and the anti-doping committees that dealt with this issue," she said.

Korakaki, 20, reveled in her milestone medal, the first of these Games for Greece, after two difficult years of training in a country struggling with a prolonged economic crisis.

"We were facing difficulties with equipment and our relationship with the federation, but I made it and qualified for the Olympics last year," she said.

"Since then, I worked really hard and I am really happy I achieved this."

(Reporting by Mary Milliken; Editing by Clare Fallon/Alison Williams/Rex Gowar)