The 2022 Wimbledon champion continued to go for broke in return games and struck a cross-court backhand winner to break for a 3-2 lead.
Serving to stay in the match at 3-5, Mertens saved one match point but could do little when Rybakina ripped yet another forehand winner on the second to clinch a place in the last eight.
With the one hour and 17 minute victory, Rybakina extended her head-to-head lead over her Belgian foe to 7-1.
Equally as self-effacing about her return game as her serve, Rybakina described it as “also not bad.”
“I had a lot of opportunities to step in on the second serve, that’s what I tried to do,” said Rybakina, who won 66 per cent of points on Mertens’ second serve.
“Overall, I think the match was a good one.”
Rybakina spends most of her time in Melbourne shuttling between the AO site and her hotel, but has carved out time to nurture a friendship with a local family that she met a decade ago whilst competing in the junior girls’ event at AO 2016, aged 16.
“When I came here for the first time, I was actually alone,” she recalled. “I remember I lost and through my aunt I met this family, I stayed in their house for I think almost for a week after.”
“They showed me a lot of nice places [and] it stays a great memory because now when I come to Melbourne, I don’t really have time to visit any places.”
“We are keeping in touch, kids are growing. It’s also funny to see how time flies and how they [have] changed.”
Her quarterfinal opponent will be decided by a highly-anticipated fourth round clash between second seed Iga Swiatek and Australian qualifier Maddison Inglis.
“I will try to recover and just play my best,” Rybakina said.