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Alongside Jan-Leppard Struff, the 25-year-old beat No1 seeds Lukasz Kubot and Marcelo Melo 6-4 6-7 7-6 to book a spot in the men's doubles semifinals.
The winning duo broke the favourites in the first game of the match, which gave them the leg up.
While Kubot/Melo broke back later on, McLachlan/Struff responded by breaking again straight away.
Both sides held their serve through both the second and third sets.
Kubot/Melo won the second-set tiebreak to force a deciding set, but McLachlan/Struff took the final set tiebreak 7-5.