It meant both sides took a point in their opening match in a tight-looking Group B, which also contains Ireland and co-hosts Australia.
Nigeria, which saw Deborah Abiodun pick up the first red card of this Women's World Cup in the dying moments in Melbourne, had Nnadozie to thank for keeping out the Olympic champions.
The 40-year-old Canada skipper Sinclair is hoping to make history by becoming the first player to score at six World Cups.
But having earned the penalty following a VAR check, she missed the chance to reach that milestone early in the second half when Nnadozie saved her poor spot-kick.
"It was a great thing today that we were able to at least get something and it was a dream come true for me personally," said the goalkeeper, who was named player of the match.
The 22-year-old Paris FC stopper said she wanted revenge on Sinclair — the all-time top scorer in international football — after conceding against the forward previously.
"When she took the ball, I was like, 'Okay, it's Sinclair again,' because the last time we played against them, she scored against me. I was very angry, and I told myself, this is the opportunity to make things right," she said
Devastated
Canada have never gone beyond the semi-finals of the Women's World Cup but are hoping to go deep into this year's tournament on the back of winning gold at the Tokyo Games in 2021.
However, they had a disrupted build-up as the team threatened to strike over pay, funding and contractual issues. They are also missing key players due to injury and perhaps continue to rely too heavily on Sinclair.
Nigeria are appearing at their ninth World Cup but were themselves embroiled in controversy in the build-up as the team clashed with their national federation over bonuses.
They had even threatened to boycott their opening game, but Randy Waldrum’s team produced a spirited performance that gives them hope of matching their run to the last 16 four years ago in France.
Star striker Asisat Oshoala was unable to shine but the Nigerian defense gave away little against the attack of the team ranked seventh in the world.
Abiodun was dismissed deep in stoppage time at the end of the game after another VAR review, a yellow card being upgraded to red. Replays showed her catching Ashley Lawrence with her studs above the ankle in a nasty challenge.
Canada coach Beverly Priestman refused to blame Sinclair afterwards and said her side must quickly dust themselves off for a meeting with the Irish next.
"This is tournament football and if I go to the Olympic Games that we won, we started with a draw, and so we've got to move on very quickly," she said."You can get lost and be really down on that, and of course the team and I am devastated that we didn't get three points."
"But at the end of the day, we got one and we took two from another team."
Australia beat Ireland 1-0 on Thursday to take early control of the group.
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