Nathan won both titles within two weeks, and he also came out as runner-up in the boy's doubles category.
"It's two weeks full of challenges and extraordinary in my tennis career," Nathan Barki said in a statement.
In the final, Nathan beat Malaysia's Jagger Zheb Chih Ong Patzwald, 6-3, 6-1.
The title complements a similar achievement in the previous week when Nathan beat the host's Jerall Yasin in the final with a score of 6-3, 6-2.
"PP PELTI is pleased and proud of Nathan's achievement in two weeks in Singapore. It's a good first step for him and hopefully it will motivate other junior tennis players to make even better achievements," Secretary General of PP PELTI (Indonesian Tennis Association) Lani Pradita Sardadi said.
In the doubles category, Nathan Barki who paired up with Brendan Nicholas Hendrata ended the tournament in second place. They lost to Singapore's Timothy Lim / Jerall Yasin with a score of 3-6, 4-6.
A week earlier, Barki and Hendrata had also lost in the final to Cameron Austin Chang (USA) / Matthew Johnstone (Australia) 6-7 (4), 3-6.
The victories in Singapore' tournament has upgraded Nathan Barki's ITF junior ranking from 782nd place as of 16 November this year to 620s, or up 150 strips, on the current world junior ranking list.
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