The 2015 SEA Games singles gold medalist relied on her superior all-court game to deal with the challenge from the 51st ranked Estonian, winning the match in 44 minutes to remain unbeaten in the group action.
"I'm very happy. I know Kuuba is very strong from the back of the court and, with her deception, at the front too. But I focused on playing one point at a time and making her run. I tried up my game for this match," said the Thai No 2.
Busanan's reward for winning the group is a daunting encounter in the last 16 knock-out round against the up-and-coming An Se-young of South Korea, ranked eighth in the world. An toppled Ajoke Adesokan Dorcas of Nigeria 21-13 21-6 to finish top of Group C. The 19-year-old South Korean, a five-time BWF World Tour winner, has won both her previous clashes with Busanan in straight games.
"She's a very strong player too. Her movement is good. I need to be ready," said the Thai.
Meanwhile, in Group D of the women's doubles, Jongkolphan Kititharakul and Rawinda Prajongjai ended their Olympic campaign in Tokyo winless with a defeat to Garbiela and Stefani Stoeva of Bulgaria 11-21 21-16 17-21.
Four Thais will be in action on Wednesday. In her final Group N match, world No 6 Ratchanok Intanon takes on Soniia Cheah Su Ya of Malaysia. The 2012 Olympic quarter-finalist must win the match to keep her hopes in Tokyo alive.
In men's singles Group K action, Thai No 1 Kantaphon Wangcharoen needs to beat Toby Penty of Great Britain to emerge as the group winner and reach the last 16.
However, a Herculean task awaits the mixed doubles pairing of Dechapol Puavaranukroh and Sapsiree Taerattanachai, as they confront 2019 World Championship bronze medalists Yuta Watanabe and Arisa Higashino of Japan in the quarter-finals. In their previous encounter at the 2019 Malaysian Masters final, it was the Japanese duo who prevailed 21-18 21-18.