It is going to go down as one of Australia's great sporting fairytale performances with the Tasmania JackJumpers beating the defending champion Melbourne United 76-73 on Monday night to book a spot in the NBL Grand Final in their inaugural season.

It is a performance from the league's newest team that just about defies belief.

They were started from nothing and had little expectations placed on them for what they could achieve this season, but coach Scott Roth from the very start wanted to create a culture where they did themselves and the state of Tasmania proud.

It's fair to say they have delivered. After winning 17 games during the regular season, they still needed a bit of luck to reach the finals in their first season. Then their challenge was a Melbourne team who claimed the regular season championship and was fighting for back-to-back titles.

Tasmania then lost Game 1 at John Cain Arena on Thursday but in front of a packed MyState Bank Arena on Saturday, rose for their home fans to win and force the decider on Monday night in Melbourne.

The occasion appeared cursed for Melbourne when captain Chris Goulding injured a calf pre-game, but this was a story all about Tasmania.

They built their success all season around playing physical, tough and tenacious defence, fighting for every single possession, making themselves mighty hard to play against and to beat, and then to do enough at the offensive end.

That became the story of their Game 3 performance. Josh Adams came up huge with 30 points but it was scoring 24 points from Melbourne's 14 turnovers, it was the critical offensive rebounds they collected and the way they made life tough for United that was the difference.

Now they can celebrate this on Monday night and prepare for Game 1 of the Grand Final Series with the Sydney Kings at Qudos Bank Arena on Friday.

Along with Adams delivering 30 points on 10/22 shooting and 7/11 at the foul line for the JackJumpers, Jack McVeigh stepped up again with 16 points with Josh Magette delivering nine points and seven assists, and MiKyle McIntosh five points and nine rebounds.

JackJumpers coach Scott Roth has been proud of his group all year and that obviously hasn’t changed now.

"Melbourne United are our champions and they showed a heart of a champion tonight after being dealt a bad blow with Chris being out, I wish he was actually in this game. We're just humble to be able to pass through them and we're better for them in the long run," Roth said.

"Our guys were gritty, tough, never gave up and it was just an incredible effort for our group. To defend the island again and impact a state like these guys have done, it's just a fantastic thing for our group and the state. I don't know what to say other than we're just blessed to be in this position and are humbled by it."

You can't underestimate the absence of Chris Goulding for Melbourne but Shea Ili was a warrior once more with 18 points, five rebounds, four assists and 7/10 shooting.

Jo Lual-Acuil finished with 16 points and seven rebounds, Jack White 14 points and 14 rebounds, Caleb Agada eight points and four boards, and Matthew Dellavedova five points and seven assists.

However, ultimately shooting 6/29 from three-point range and 11/21 at the foul line proved costly.

There wasn’t much for Melbourne coach Dean Vickerman to say afterwards other than tip his cap to the JackJumpers.

The meeting that you have with players and staff when your season's finished and you don't achieve what you want to achieve is always a really challenging meeting because you know that group's not going to be together in its entirety again.

There's a lot of disappointment and when you talk about the game, we had good runs but we also had some down patches, and the one down patch was at the start of the third and end of the fourth that got them a pretty hefty lead.

We still made a fight back and I can't question some of those areas of the game, but we'd done a good job on Adams in the series and then he has 21 in the second half. Credit to him, he's a pretty tough kid and credit to that whole team. I hope they go on and really challenge Sydney in the Grand Final.

Despite not having their captain out there, Melbourne started well with the first five points of the game through Jo Lual-Acuil and Jack White. While Josh Magette got Tasmania on the board, Shea Ili put United up 7-2 and then Agada made it 9-2.

Tasmania weren’t rattled, though, and worked back into it going on a 12-2 run starting with a three ball from Fabijan Krslovic and then an and-one play from Sam McDaniel against the team he helped win the championship a year ago.

Melbourne responded with the next eight points with three-point bombs from Brad Newley and Yudai Baba, and that helped the defending champs go into quarter-time leading 25-21.

The JackJumpers opened the second period with a triple from Jarrad Weeks and then Josh Adams got aggressive for the JackJumpers. He took the ball to the rack and got to the stripe a couple of times and scored nine points as part of a run of scoring 14 of 19 points.

Jack McVeigh's corner three had the JackJumpers up four but by half-time scores were locked at 40-40.

The JackJumpers were believing and opened the second half with the first five points and two sloppy United turnovers had coach Dean Vickerman irate.

His team responded to a standing timeout with the next six points, but Tasmania just wouldn’t be denied. Adams was in the zone and took it to the rack for a couple more finishes before draining a pair of three balls to give the league's newest team a nine-point lead.

They were still up six by three quarter-time and there was no way Melbourne wasn’t going to throw everything at it. And on the back of three big plays from Lual-Acuil, the regular season champs were back up one with 6:40 left.

This was a JackJumpers team that has risen to all challenges all season, though, and they weren’t about to stop now. Not even against the defending champs, not even away from and not even with nobody having had any expectations for them.

They were back on top six following three balls from import guards Josh Magette and Adams, and Adams was able to finish the job at the charity stripe and the most unlikely of Grand Final appearances was a reality.

HUNGRY JACK'S NBL FINALS – SEMI FINALS GAME 3

MELBOURNE UNITED 73 (Ili 18, Lual-Acuil 16, White 14)

TASMANIA JACKJUMPERS 76 (Adams 30, McVeigh 16, Magette 9) 

Tasmania wins best-of-three series 2-1

BOX SCORE