The US Open champions ended up beating China's Saisai Zheng and Belgium's Joran Vliegen in a 6-3, 6-4 win to continue their run in Melbourne.
It wasn't easy for them though as they had to save six break points, including two while they were serving for the match.
It is a first for Murray who has never reached the last four in Melbourne but Mattek-Sands on the other hand claimed the title in 2012 with Horia Tecau.
As well as their win over their fellow unseeded duo, they have also defeated Leander Paes and Jelena Ostapenko and number one seeds Marcelo Melo and Barbora Strycova.
https://twitter.com/TeamGB/status/1222507383886356480?s=20