Chartvanchai took ill with a high fever. Chartvanchai was down three times before finally being called out for the full count. Enrique Jimenez refereed. Oba finished off Chartvanchai with a volley of punches to the head at 2:16 into the thirteenth round. Charvantchai had trouble making the weight limit, even after doing light exercise and taking a steam bath, which may have weakened him for the bout. Oba gained a considerable lead in points throughout the match. Chartvanchai was weakened both by a cut to his eye he received in the fourth round which gave him trouble and the efforts he took to make weight. First four defenses of the WBA World Flyweight Title On January 21, 1971, he defeated Swiss boxer Fritz Chervet in a non-title fight technical knockout at Korakuen Hall in Tokyo, Japan. The bout was ended after 1:31 into the eighth round. Ohba made his first three WBA World Flyweight Championship defenses by 15-round decisions, and his 4th defense by 5th-round KO, all at Nihon University Stadium in Tokyo. He also fought four non-title matches in between his defenses, winning all of them as well. His first defense was against the great champion Betulio González on April 1, 1971, in Tokyo in a very significant fifteen round Unanimous Decision. González would hold the Venezuelan Flyweight Title, and at one time hold both the WBC and WBA World Flyweight Championships. On August 19, 1971, he won a Unanimous Decision over Tony Moreno of San Antonio in a non-title ten round bout. The audience of 2000 were somewhat disappointed as Ohba was unable to score a knockdown against his opponent. His second defense of the World Flyweight Title was also a fifteen-round Unanimous Decision on October 23, 1971, against Filipino boxer Fernando Cabanela. His third defense was against Japanese boxer Susumu Hanagata on March 4, 1972, in a fifteen-round mixed decision in Tokyo. Hanagata, an accomplished flyweight, would briefly take the WBA World Flyweight Title in October 1974. His fourth WBA World Flyweight defense was against Orlando "Yango" Amores from Colón, Republic of Panamá, on June 20, 1972, in Tokyo. Ohba impressively won on a fifth-round knockout. Last fight, fifth defense of WBA World Flyweight Title On January 2, 1973, Ohba faced the Thai veteran boxer, Chartchai Chionoi, for his fourth defense. Ohba was knocked down with a right hook in only forty seconds into the first round,