Mills starred in the second half with an outstanding performance from the bench to lift the Spurs to a 104-87 win over the Miami Heat in San Antonio on Monday.

The former Canberra Marist College student and teammate Aron Baynes are the third and fourth Australian's to win the biggest prize in world basketball, joining greats Luc Longley (Chicago Bulls) and Andrew Gaze (San Antonio).

Mills is the first indigenous Australian to win an NBA championship.

The 25-year-old got the Spurs out to a championship-winning lead in the third quarter with sublime three-point shooting. He went on a destructive 11-point run in five minutes to get the Spurs' lead to 20 points.

All up, he scored 17 points in his 18 minutes on the court, shooting six for 10, including five of eight three-pointers. Mills also threw in a rebound and two assists. The Spurs outscored the Heat by 15 points while he was on the floor.

"The support has been great all year," an elated Mills told San Antonio reporters.

"The community of San Antonio has been great, you know how important you guys are to us.

"You're a part of this win, as much as anyone. I can't tell you how nice and genuine the people of San Antonio are compared to anyone else, it reminds me a lot of Australia.

"This one is for you [the fans] and thanks for all your support."

The championship-win caps Mills' rise from towel-waving benchwarmer to genuine NBA contributor.

He played just 13 minutes in the NBA finals last year.

But after an off-season fitness regime and hiring a personal chef to help him get in the best shape of his career.

"His energy has been important all season long. That energy, that team sense he has, has become infectious for everyone," said Spurs coach Gregg Popovich.

However, the fact Mills is most proud of is the way awareness that has been created for his culture and family.

Mills' mother Yvonne was part of the Stolen Generation and dad Benny is a Torres Strait Islander. Mills' uncle Danny Morseu, who was the first indigenous Australian to play basketball for Australia at the Olympics, is also in San Antonio for the game.

After barely playing in the Spurs' agonising 4-3 loss last season, the sharp-shooting Mills has been a vital cog in their line-up throughout the season and stepped it up in game five, helping them to an emphatic 4-1 series win.

The Canberra-born point guard, an energetic towel-waver and garbage-time regular last season, had three points in the first half but exploded for 14, including four three-pointers, in the third quarter.

He did not score again, his 17 points taking his series tally to 51 in comparison to the four he scored last year.

Now off-contract, Mills can expect a number of more lucrative offers in the off-season after a strong 2013/14.

Mills's contribution was just what was needed for the Spurs as starting point guard Tony Parker was struggling with his shot, going 0-10 from the field to start the game.

Frenetic defence was a regular feature of Mills's game-five effort, taking his turn slowing down Heat superstar LeBron James (31 points), Dwyane Wade (11 points) and 2013 hero Ray Allen (five points).

The Australian's third-quarter heroics came on the back of a remarkable San Antonio comeback.

James scored 17 points to carry his team to a 22-6 lead after seven minutes.

It looked a promising response to the Spurs' demolition of the Heat in games three and four, but a huge second-quarter run, sparked by Argentine bench star Manu Ginobili (19 points), saw the Spurs take a 47-40 lead into half-time.

The Spurs have now won five championships since 1999.

Since drafting the Hall of Fame-bound power forward Tim Duncan (14 points, eight rebounds) in 1997, the Spurs have won at least 60 per cent of their games in every season.

He was joined in San Antonio by Ginobili in 1999 and Parker in 2001, forming arguably the most successful 'Big Three' in NBA history.

The Spurs won the title in 1999, 2003, 2005 and 2007 (a sweep over James's Cleveland Cavaliers) but this year's title took on special significance.

The Heat took down the Spurs in last year's Finals with a miraculous comeback win of their own in game six and a tight victory in the deciding game seven.

There were questions in the preseason as to whether the Spurs, boasting a number of players in their mid to late-30s, could rebound from such a brutal loss, but those questions were answered in spades on Monday.

It is also the fifth title for three-time NBA Coach of the year Gregg Popovich who joined the team in 1996, but the future in San Antonio looks in good - and very large - hands.

For the third consecutive game in this series, small forward Kawhi Leonard, nicknamed 'Big Hands', was the Spurs' top-scorer.

The third-year star's spectacular scoring outbursts, as well as his remarkable effort defending James, secured him the Bill Russell trophy as the Finals MVP.

He averaged 17.8 points and 6.4 rebounds for the series and, at just 22 years of age, Leonard is the youngest man to receive the honour since 1999, when Duncan, then 23, took the trophy.

Duncan was in just his second NBA season when he was first named Finals MVP and went on to win it in 2003 and 2005.