The 14-year-old belied his young years to defeat the top seed in six games at the OMEGA Sport Center in Olomouc.

He came from 2-1 behind to triumph 11-3, 4-11, 8-11, 11-9, 11-6, 11-9.

Boll was aiming for a 20th World Tour title but it was Harimoto who etched his name into the history books.

Harimoto was already the youngest player to reach the main draw of a World Tour event, which he remarkably did aged just 12 in 2015.

He has now broken the record of China’s Yu Ziyang, who was 16 when he won the Japan Open in 2014.

"Age doesn't matter, you must play and fight against everyone," Harimoto said.

"It was my second World Tour final, first time I lost my chance, this time I won. 

"Now at the Tokyo 2020 Olympic Games I want to win men's singles and men's team gold but I know I must practice hard and fight to gain the glory."

In the women's final, Mima Ito turned the tables on Kasumi Ishikawa in an all-Japanese affair.

The same players met in the final of last week's Bulgarian Open which Iskikawa won.

Ito took her revenge against the top seed today, 11-5, 15-13, 11-3, 9-11, 11-4.

It turned out to be a double celebration for Ito as she teamed up with Hina Hayata to win the women's doubles.

They beat Georgina Pota of Hungary and Matilda Ekholm of Sweden 11-5, 8-11, 8-11, 11-6, 11-8.

"Last week at the Bulgarian Open, I won the doubles, but finished second in the singles," said Ito. 

"This time I was able to win doubles and also singles; so I feel very happy, but I am also very tired."

Germany's Patrick Franziska and Denmark's Jonathan Groth won the men's doubles title, seeing off Japanese duo Jin Ueda and Maharu Yoshimura 11-6, 8-11, 11-9, 11-8.