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Adams, 33, beat China's Ren Cancan - who she beat to win gold at London 2012 - in Thursday's semi-final.
The Leeds woman lost the first of four two-minute rounds, before coming back to win the final three.
She will face France's 10-time national champion Sarah Ourahmoune in Saturday's gold-medal match (18:00 BST).
"Another gold-medal fight - I can't wait. This is what I've been training for for the last four years. I'm excited," she told BBC Sport.
It is guaranteed to be GB's first gold or silver boxing medal at Rio 2016, although super-heavyweight Joe Joyce could also reach his final.
The 30-year-old Londoner meets Kazakhstan's Ivan Dychko in Friday's semi-final ahead of Sunday's gold-medal bout.
Defeated semi-finalists do not fight again and both receive bronze medals.
Joshua Buatsi won Team GB's first boxing medal in Brazil by securing bronze at light-heavyweight.
Adams has achieved virtually everything there is to achieve in boxing, having already won Olympic, European and Commonwealth golds.
But she showed her determination to add another Olympic title - becoming the first Briton to defend her crown after middleweight Harry Mallin in 1924 - by coming from behind against Ren.
Ren, a three-time world champion, took the opening round on all three judges' scorecards, but Adams came out aggressively in the next to pin back her 30-year-old opponent with her powerful left jab.
She knocked Ren off balance as she restored parity at the halfway stage, also going on to win the final two rounds 10-9 across the board.
"Four years is a lot of time to for a boxer to change and strengthen their weaknesses so I just had to go and stick to the tactics," Adams said.
"The jab won me the fight, it just paid off. I am always nervous and you need that nervous energy to give you the adrenaline."
Anthony Joshua, 2012 Olympic super-heavyweight champion on BBC TV:
"I am sure Nicola will be familiar with Sarah Ourahmoune - the French and British spar a lot together.
"I think Nicola will control her with jabs and keep busy to not give her an opportunity to attack."

Three women and a man were treated for the effects of breathing in smoke following the fire in Murrayburn Green, Sighthill, on Sunday night.
It is thought abandoned furniture was deliberately set alight in the building's common close at about 21:00.
Two of the woman were taken to hospital for medical checks. A total of eight homes had been evacuated.
Police said they were keen to speak to anyone who could help them trace those responsible.
Insp David Ferguson of Corstorphine Police Station said: "Thankfully no-one was seriously injured in this incident but it could have been much worse.
"I am keen to hear from anyone who was in the area around 21:00 on Sunday night and who might have information that can assist us with our inquiries.
"I'd also like to remind residents not to leave items of furniture or rubbish in communal areas where they can be a target for fire-raising."

Sidwell made 34 league appearances last season as the Seagulls returned to the top flight after a 34-year absence.
The 34-year-old joined Brighton on an initial loan deal from Stoke in January 2016, before joining the club on a free transfer ahead of last season.
"Steve has been a key member of the squad over the past 18 months," manager Chris Hughton said.
"Our fans know his qualities well, and his experience, particularly at Premier League level, will be important for us."
Nicola Adams continued her bid to become the first British boxer to retain an Olympic title for 92 years by reaching the women's flyweight final.
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A blaze at a block of flats in an Edinburgh housing estate was started deliberately, police believe.
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