"The people of the Cook Islands have all been there on the journey with me, supporting, loving, caring, building our community to get me here," the delighted 26-year-old said early today.
It's the first time a Cook Islander has achieved such a feat on the stage of the international beauty pageant, and Sahay was absolutely delighted.
She was also crowned Miss Oceania. On her way to the top 12, she had excelled in the sports and talent sections, where her traditional Cook Islands dance earned critical acclaim.
Holding a Cook Islands flag, she thanked her supporters and all Cook Islanders: "Kia orana, we have just won Miss Oceania," she said. "I could not be more appreciative. Meitaki ma'ata!"
Miss Jamaica Tony-Ann Singh was crowned Miss World 2019, and Miss India Suman Rao beat Sahay for runner-up.
Sahay's support team at the ExCel Centre in London, led by mother Ruth Sahay, sister Yaleisha Shanasa and Miss Cook Islands organiser Rohan Ellis, were even more ecstatic than she was.
Just before the pageant, Tajiya Sahay was nervous, but still able to laugh. "Popongi! Haha I only have one fear today and that's falling over in my heels but other than that I'm more excited than nervous," she told Cook Islands News.
"This is what we have been working towards, this is what we have been looking forward too. Let's embrace it and make the most of it! Let's enjoy every moment because this is a once in a lifetime opportunity.
"I'm very excited. And I guess if I fall, I fall. I'll just laugh it off!"
Last year's Miss Cook Islands, Reihana Kotika-Wiki, sent her congratulations from New York. "Tajiya Sahay is Miss World Oceania! Huge congratulations to Miss Jamaica for being crowned Miss World. We are so proud of you Taji! History has been made!"
Ahead of the final, Sahay had thanked supporters for sending her on "such an unforgettable, once in a lifetime journey and most importantly, given me the chance to represent my beautiful Cook Islands."
Tickets to today's final ranger from £27.50 (NZ$56) for a seat obstructed by a pillar, up to £220 (NZ$444) for a VIP seat near the front.
Sahay had the best position in the House – up on the stage. But the fitness trainer has had to pay the most as well, sacrificing months of her life to the dream.
On winning Miss Cook Islands two months ago, she revealed to Cook Islands News her brave journey from shy, "borderline obese" teenager to a trainer working with youth to help them discover healthy diets and fitness.
"It's not easy for a little Island locked away in the south Pacific to be able to accomplish something as big as preparing for Miss World, but we did it. With the help of our generous community and encouragement of the association, we did it."