In a huge confidence-booster, Joint upset 2020 Australian Open champion Sofia Kenin 7-6 (7-3) 6-4 at Memorial Drive on Tuesday.
The Aussie No.1 fired down six aces and broke the American world No.28 three times while also saving six of the eight break points she faced in a particularly strong service display in her third consecutive win over Kenin.
"I knew that she likes to serve a lot out wide, so I just needed to hang on that serve on the deuce side," Joint said of her shrewd tactics.
"I targeted her forehand a bit more because her backhand's, I think, stronger. So I tried to make her move, mix up some spins.
Sofia played really well today. I'm just really glad that I was able to stick in, fight through it and just find a way to play some really good tennis in the important moments."
Joint trailed 4-1 in the second set but was able to mount an impressive comeback to seal victory in one hour and 38 minutes.
"She was playing some great tennis. I had to problem solve a little bit," the 19-year-old said.
"I was having some problems on my return. She was really hitting her spots on her serve. So I just needed to find a way to neutralise her serve."
Set to be seeded for the first time at a grand slam at next week's Australian Open, Joint's win came after two straight-sets losses to multiple grand slam champions Barbora Krejcikova and world No.2 Iga Swiatek at the season-opening United Cup in Sydney.
"I re-watched the matches against both of them. They were playing pretty good tennis both days, so it was two tough matches," she said.
"My coach and I went over some small details that I could have improved just to make the match a bit closer.
"I've been working a lot on my serve placement and just accuracy."
Joint started the year with a nasty bout of the flu, which forced her to sit out Australia's opening tie against Norway.
"Yeah, I'm all good now," she said.
"I only felt bad for maybe a week, so I feel good."
Tomljanovic booked her place in the second round on Monday when Danish fifth seed Clara Tauson retired injured after losing the opening set in a tiebreaker.
Despite being ranked 44 spots below the world No.32, three-times grand slam quarter-finalist Tomljanovic has won two of her previous three meetings with Joint.
"It's always tough playing a friend," Joint said.
"We've had pretty good matches each time. Always difficult having to play someone that you know, playing another Aussie.
"The crowd's going to be amazing. The atmosphere's going to be really good.
"So I'm excited."
The winner could face Mirra Andreeva in the quarter-finals after the Russian top seed opened her tournament on Tuesday night with a resounding 6-3 6-1 win over Czech Maria Bouzkova.
In further good news for the locals, Australian wildcard Kim Birrell also advanced to the second round with a 6-4 6-4 win over Russian-born Austrian qualifying lucky loser Anastasia Potapova.
Birrell next faces Czechia's former Wimbledon champion Marketa Vondrusova for a place in the last eight.
With Daria Kasatkina also progressing on Monday, Australians make up a quarter of the second-round players in the South Australian capital.
