The pair outgunned Japan's 10th-seeded Shuko Aoyama and Ena Shibahara 6-4, 6-3 to post their 24th straight win at a major after triumphing last year at the Australian Open, Wimbledon and US Open.
Top seeds Barbora Krejcikova and Katerina Siniakova won their fourth Grand Slam Sunday, sweeping to the Australian Open women's doubles title against Kazakstan's Anna Danilina and Brazilian Beatriz Haddad Maia.
Ashleigh Barty set up a clash of French Open winners in the Last 16 of Wimbledon after the world number one beat Katerina Siniakova of the Czech Republic 6-3, 7-5 on Saturday.
Australian Open 2021: Second seeded Elise Mertens and Aryna Sabalenka defeated third-seeded Barbora Krejcikova and Katerina Siniakova 6-2, 6-3.