Saville, on the comeback trail after returning to the tour in June from a serious knee injury, lost to world No.29 Mertens 6-4 4-6 7-5 in the semi-finals on Friday.
A wildcard entry, world No.195 Saville knocked out three top-50 players in Hobart, including 2020 Australian Open champion Sofia Kenin and China's world No.33 Zhu Lin.
The 29-year-old was granted wildcard entry to the main draw at the first grand slam of the year and will meet Poland's world No.72 Magdalena Frech in the first round.
Saville, who has previously reached the world's top 20, went toe-to-toe with Mertens.
Remarkably, both players won 37 points in the first set and finished on 100 points won for the match.
Saville was down a break early in the deciding set but rallied to level at 3-3 before dropping serve in the second-last game.
"It was a great level. I'm proud of myself," Saville said.
"I got a bit nervous in the end, maybe a lack of playing semi-finals. But overall it was a great week.
"I can build on that and I'm excited for more.
"It is going to be exciting to play at home (at Melbourne Park). It's my favourite time of the year."
Mertens said Saville had improved since their previous meeting in October in Hong Kong, which went the way of the Belgian in straight sets.
"I knew it was going to be difficult, Daria is a very good player," Mertens, who is chasing her third Hobart title after success in 2017 and 2018, said.
"It could have gone either way, a lot of 40-all. It was high-quality tennis.
"She is really improving. She's hitting the ball a bit harder, less mistakes too."
Mertens will meet either second-seeded American Emma Navarro or Chinese qualifier Yue Yuan in Saturday's final.
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