* Chen records season best in short programme
* Olympic champion Hanyu rues "little" mistakes
* World champion Medvedeva maintains dominance (Recasts with women's short programme)
MOSCOW, Oct 20 (Reuters) - Nathan Chen of the United States stunned reigning world champion Yuzuru Hanyu of Japan in the grand prix season opening in Moscow by taking first place in the short programme, while two-time world champion Evgenia Medvedeva again showcased her dominance of the women's circuit.
Chen recorded a season-best performance of 100.54 points at the first of six events to qualify for the Grand Prix Final in Japan in December, which comes barely two months before the start of the Winter Olympics in Pyeongchang.
He had two shaky landings on his quad flip and triple axel jumps. He made up for it, however, with a spectacular combination of the quad lutz and triple toe loop.
"In terms of the programme, I'm happy with the scores that I got," Chen told a news conference. "I'm going to have a lot of work going into the Games. But as of now I'm happy with what I did and just have to keep my mind straight and keep working hard."
Hanyu, the defending Olympic champion, made a difficult landing on the quad loop jump at the start of his programme before falling on his triple toe loop, earning him 94.85 points.
The 22-year-old – who set a short programme record score of 112.72 points last month — told reporters that "just little things" had gone wrong and that he was eager to refocus for Saturday's free programme.
"I feel really close to success," Hanyu said. "I will just fix those things for tomorrow. I will recover. I will do better tomorrow."
Dmitry Aliev of Russia, who was taking part in his first senior grand prix, finished third with 88.77 points.
Kazakhstan's Denis Ten, who won bronze at the 2014 Sochi Olympics, finished 10th with 69.00 points after a disappointing performance that saw him stumble on his quad salchow and fall on his triple toe loop.
Ten suffered an ankle injury earlier this year and underwent extensive rehabilitation, setting him back in his preparations for the Games next year.
On the women's side Medvedeva – a two-time world and two-time European champion - skated a programme full of grace and technical skill, earning her first place in the short programme with 80.75 points.
"I'm pleased with my skate but there were some nuances that I didn't like, mostly about my focus," the 17-year-old said.
Italy's Carolina Kostner, 30, finished second with 74.62 points -- her highest score since the 2014 world championships.
Kostner has been fighting to make up for lost time since she was banned for 16 months in January 2015 after Italian officials found her guilty of assisting 2008 Olympic race walking gold medalist Alex Schwazer in evading a drugs test.
"The work in coming back to competitive skating, or continuing in competitive skating, has been a long and difficult process," Kostner said.
"I don't think it's finished yet. The roof is very much open and I'm very looking forward to where I can go."
Mirai Nagasu of the United States could have challenged the leaders when she landed a triple axel but she fell on her triple toeloop and triple lutz, mistakes that saw her finish ninth with 56.15 points.
In pairs, Russia's Evgenia Tarasova and Vladimir Morozov led the pack with 76.98 points.
Their compatriots Ksenia Stolbova and Fedor Klimov, who won silver in the Sochi Games in 2014, came in second, scoring a season-best 71.39 points even though Stolbova fell on her triple toe loop.
"We think we skated well apart from one mistake that we consider accidental," Klimov told reporters.
American brother and sister duo Maia and Alex Shibutani -- who won bronze at the world championships this year -- dominated the short ice dance, finishing first with 77.30 points.
Russian ice dancers Ekaterina Bobrova and Dmitry Soloviev finished close behind with 76.33 points. (Reporting by Gabrielle Tétrault-Farber; Editing by Christian Radnedge/Rex Gowar)