Thailand's Kunlavut spills blood to win badminton world crown
The 22-year-old world number three, who was runner-up a year ago, is the first Thai to win the men's singles title at the World Championships.
World number four Naraoka, also 22, put Kunlavut through an excruciating match of marathon rallies that lasted 109 minutes on Sunday -- one of the longest men's singles matches ever.
Kunlavut's blood had to be wiped off the court several times as he threw himself around to keep the shuttle alive in a series of lengthy rallies.
"I'm very happy, this has been a dream for me since I was a child," said an emotional Kunlavut.
"When I was young I'd promised my coach that I would get the gold medal. He passed away and I dedicate this gold medal to him.
"I had three targets when I was young -- Olympic Games, world championships and All England (championships). Now I have achieved one of those, so two are left."
It was the second longest world championships men's singles final, eclipsed only by the 124-minute epic between China's Sun Jun and Denmark's Peter Rasmussen in the inaugural world championships in 1977.
"I needed to be prepared for a long match with Kodai," added Kunlavut.
"We know each other's game because we have played since our junior days. You have to be very patient with him and it was very tiring, so I didn't have any energy left to celebrate."
South Korea's world number one An Se-young enjoyed a more straightforward march to the women's singles title when she beat Spain's Carolina Marin 21-12, 21-10 in the final.
The top seed, who becomes South Korea's first women's world champion in the 46-year history of the event, sped to the title in just 42 minutes.
"I am the champion. I am so happy today," An said.
"I think I played well today because I enjoyed myself out there. I had so much fun."