The 19-year-old Lakshya from Almora, who had claimed five titles in 2019, saw off France's Thomas Rouxel 21-18 21-16.
HS Prannoy said he did some online sessions with European players during the two weeks in Thailand to keep himself fit.
Thailand Open: Shuttler HS Prannoy cruises to second round after hard-fought win vs Jonatan Christie
In the first game, Christie defeated Prannoy 18-21 but in the following two games, the 28-year-old put on some fine performances and ensured his spot in the second round.
Saina was in fact staring at a 10-day isolation at a local hospital. But all three of them, including Kashyap and Prannoy, underwent antibody tests later.
Saina Nehwal, HS Prannoy test negative for COVID hours after positive results, cleared for Thailand Open
Saina Nehwal and HS Prannoy on Tuesday tested negative for COVID-19 hours after returning positive results.
A walkover was given to Kisona Selvaduray of Malaysia, who was to play her first-round match of the Thailand Open against Saina on Tuesday.
The attention has now turned to Denmark Open, but Prannoy, who chose to skip the event, feels that there might still be some reluctance from players due to a lack of clarity about safety measures.
HS Prannoy will start his tournament with a second-round clash with the winner of the match between Mauritius' Paul Christopher Jean and Seychellois Steve Malcouzane.
Saina Nehwal defeated Line Hojmark Kjaersfeldt of Denmark 21-14, 11-21, 21-10 in 50 minutes at French Open.
Saina staved off a spirited challenge from World No 44 Mette Poulsen of Denmark 21-19 23-21 in a 46-minute match.