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Just a month after changing to compete under the Japanese banner, the 25-year-old has won the Japan Open and netted a $100,000 pay day.
Alongside fellow Japanese player Yasutaka Uchiyama, McLachlan claimed victory in the men's doubles on Sunday night.
In doing that, the duo beat the second-seeded 2016 US Open champion pairing of Briton Jamie Murray and Brazilian Bruno Soares 6-4, 7-6 in the final.
They also toppled the most recent US Open doubles champions, top seeds Jean-Julien Rojer, of the Netherlands and Romanian Horia Tecau in the quarterfinal.
The tournament is a 500-level one and rates highly, a step up from the 250-level ASB Classic in Auckland.
Only the four grand slams and nine masters events are bigger in world tennis.
McLachlan's coach, brother Riki, said Ben was excited with the win.
''He's pumped. It's been a crazy week capped off with a win, so he's excited.
''Just an awesome experience too, to get out there with some of the best teams and just a huge home crowd too. He played very well.
''He played great that week, just a different level of confidence and having the energy from the crowd really helped too.''
McLachlan qualified for Japan through his mother and switched allegiances as it would be likely to provide better opportunities.
That had allowed him to gain entry to the event via one of two wildcard spots for locals.
He had also represented the country at the Davis Cup, which was something he had not done in New Zealand.
''It's been a crazy time so far. He's had an amazing run,'' Riki said of the switch.
''Getting picked for the Davis Cup I think is a huge boost for him and just the confidence and experience.''
Riki remains based in Queenstown and coaches Ben over Skype in order to get around the cost of having a coach on tour.
He said that was not always easy, as Ben was on the road a lot more, although he hoped that time travelling would keep increasing.
Ben had another five weeks on tour, before returning to New Zealand, where he would spend a month over summer preparing for next season.