Tonga scored seven tries in total in the game against Romania, with winger Solomone Kata claiming a double, one in each half.
They also dedicated the win to their fans and families.
Kefu, who has been at the helm for the Tongans since 2016, told the media at the post-match press conference it was an emotional game for him and the players, adding he was pleased for the team.
He hoped the momentum could continue and that more was done to help Tonga and other Tier-2 teams to get more game time together.