The Spanish Rio 2016 gold medallist, a three-time world champion, has endured eight months on the sidelines after ACL surgery and only returned to competition last week.

She is unseeded at the Olympic Sports Center Xincheng Gymnasium in Changzhou and was handed a tough opening clash with Japan's Okuhara, the fourth seed who lost the World Championship final to India's PV Sindhu last month.

Marin, who won the China Open last year, lost her first-round match on her comeback in Vietnam but demonstrated a return to form as she beat Okuhara, the 2017 world champion, 21-16, 21-18.

"Of course I feel really happy with how I could play today," said Marin. 

"I just want to forget about my injury. 

"I missed a lot of tournaments and playing at a high level with good players. 

"Of course I was ready for this game. 

"My physical condition is really good, my knee is really good, I don't have any pain. 

"I feel more confident about that. 

"I just have to keep focus on my mental game. 

"Because when you play a top player it is tough, to be focussed through the full game, but today I did really great.

"Last week, it was my first game and of course I felt some nervousness and tension that I would like to win my first game. 

"That made me feel more tension with my body and I couldn’t think about what I had to do with my opponent. 

"But today I just wanted to think about what I had to do with Okuhara."

Other women's matches on day one of the prestigious World Tour Super 1000 tournament included a major shock as the 2017 winner in China and top seed, Akane Yamaguchi, lost a thriller to Russia's Evgeniya Kosetskaya.

In a tight contest, Kosetskaya lost the first game, but fought back to win 20-22, 21-17, 24-22 and blow the tournament wide open.

Thailand's 2013 world champion Ratchanok Intanon, seeded sixth, beat Denmark's Line Kjærsfeldt 21-17, 21-17, while China's seventh seed He Bingjiao beat compatriot Han Yue 21-18, 21-17.

In the men's draw, back-to-back and reigning world champion Kento Momota won an all-star first round clash with China's double Olympic gold medallist Lin Dan.

Japan's top seed came through 21-14, 21-14 against his 35-year-old opponent, the Beijing 2008 and London 2012 gold medallist who is no longer at the peak of his powers.

Momota is hoping for a first victory at the China Open, a title Lin has won five times.

There was better fortune for the hosts as reigning Olympic champion Chen Long won in three games against Malaysia's Lee Zii Jia, 21-16, 12-21, 23-21.

The fourth seed is bidding for a fifth China Open victory.

Denmark's 2017 world champion Viktor Axelsen was beaten on his return to action following injury.

The sixth seed, who announced in July that he would be taking an "indefinite break" from the sport, made a flying start but lost 10-21, 21-14, 21-16 to Japan's Kanta Tsuneyama.

The remaining first round matches in the men's and women's draws will be held tomorrow.