The Thai fourth seed defeated Yeo Jia Min of Singapore 21-15, 21-15 and will face Yvonne Li of Germany for a place in the women’s singles quarter-finals.
Li strolled past Hadia Hosny of Egypt 21-7, 21-9 in just 19 minutes.
“My performance today was quite good. Not 100 percent but I am proud of my performance. My fitness is strong which I’d like to keep maintaining,” said Ratchanok.
Fifth seed Carolina Marin of Spain also got off to a winning start, beating Qi Xuefei of France 21-10, 21-12 to progress.
The reigning Olympic champion will next face Thai hope Pornpawee Chochuwong, who beat Neslihan Yigit of Turkey 22-20, 21-13.
“I feel really happy to be back on court after some months without tournaments. I have really missed it a lot,” said Marin. “Winning here is what I want. I would like to win a title here. We can’t interact with the other players because of the strict bubbles, but it’s so nice to see the players from all the other countries.”
Another Thai hope Supanida Katethong also advanced with a 21-14, 21-16 victory over Ruselli Hartawan of Indonesia. She will next play Evgeniya Kosetskaya after the Russian eased past Thailand’s Natchanapon Roongpiboonsopit 21-12, 21-9.
An Se-Young of South Korea became another seeded player to progress without much trouble. The seventh seed needed just 38 minutes to defeat Soniia Cheah of Malaysia 21-15, 21-12.
An will play 15-year-old Thai Sirada Roongpiboonsopit for a place in the quarter-finals. Sirada received a walkover from Doha Hany of Egypt.
India’s Saina Nehwal also moved into the second round after beating Kisona Selvaduray of Malaysia 21-15, 21-15.
In the men’s singles event, Daren Liew of Malaysia claimed the biggest upset so far after he knocked out third seed Anders Antonsen of Denmark 21-12, 21-18.
“I am actually surprised. I think I played quite well. Before this tournament I didn’t know I would even play because I was on the reserves list, so to make it at the last minute and also win my first round against the third seed, it has really surprised me,” said Liew.
Antonsen said: “Daren played a good match. He was the better player. I was a bit surprised by my performance, but not by Daren’s. I hope I can play better next week.”
Second seed Chou Tien-chen of Taiwan survived a tough challenge against Thai veteran Tanongsak Saengsomboonsuk.
The former world No.9 raised hope of an upset after taking the first game 21-16 but the Taiwanese star fought back to take the next two 21-10, 21-14.
“I was a bit nervous but in the second game I regained my speed and confidence,” said Chou. “He [Tanongsak] played really well at the net in the first game. I had to change my plan and move him and improve my attack and control to open the point up.”
Seventh seed Angus Ng Ka Long of Hong Kong also moved safely into the last 16 round following his 21-15, 21-16 win over Mark Caljouw of the Netherlands.
In the women’s doubles event, Thai duo Puttita Supajirakul and Sapsiree Taerattananachai defeated Setyana Mapasa and Gronya Somerville of Australia 21-11, 21-9.
Men’s doubles Thai pair Supak Jomkoh and Kittinupong Kedren also came through their opener, defeating Mark Lamsfuss and Marvin Seidel of Germany 23-21, 21-19 in a tight contest.
The Yonex Thailand Open is the first of three consecutive tournaments in the Asian leg of the BWF World Tour held behind closed doors.
The tournament, which ends on Sunday, will be followed by the Toyota Thailand Open from Jan 19-24.
Both are Super 1000 tournament with a total purse of $1 million each.
The season will conclude with the $1.5 million HSBC BWF World Tour Finals 2020 (Jan 27-31).