"Emotionally, I'm really exhausted now," she said in her post-match press conference.
Svitolina recently hired former No.1 Justine Henin as part of her coaching team, and the Ukranian has enjoyed a flying start to their partnership with a run to the semifinals at the Dubai Duty Free Tennis Championships and was looking for her first title of the season in Kuala Lumpur.
There were few signs of the rain-interrupted epic this match would become at the start, and Bouchard, who is in the midst of a resurgence following a disappointing 2015, broke through after the first rain delay to win the first set in a tie-break.
"It was a long day. The first set was really tough and she was playing really well, but I was 5-3 up, so I was disappointed to lose the first set after such a tough fight. After we stopped a couple of times because of the rain, it was up and down."
Svitolina had never lost to the Canadian in three prior meetings, and her frustration at failing to serve out the opening set shown through as she fell behind 4-2 in the second. The No.2 seed soon caught fire once more, winning the last four games of the set to level the match before rain came once more.
"Honestly, I don't remember much of the second set now because my emotions are over the moon. I just remember that it was so tough and I was 2-4 down and came back to win that set.
"During the match, I tried to change something in my game plan; I tried to adapt. When I'm not winning, why should I do the same thing?"
Bouchard looked to have the momentum when it counted, emerging from the final interruption to serve for the match in the tenth game. But the former Wimbledon finalist lost serve to love and Svitolina, who was forced to save a break point at 5-5, engineered an efficient service break to clinch the victory just before midnight.
"Many people would think the match is over, but I like to surprise everyone," she said with a laugh. "Honestly, I was just trying to play my game; there was nothing special, just when I lost my serve I was 30-0 up, and emotionally I was struggling a bit because I lost my serve in such a big moment.
"I said to myself that I needed to just play my game and forget everything that happened in the last game. I did a great job; I played amazing returns, and she was really under pressure. This was the key in that moment."
Winning in Kuala Lumpur brings Svitolina up to a career-high ranking of No.14, and back into the Top 15 for the first time since last summer.
"Thank you very much for staying that late to watch our final," Svitolina said in her victory speech. "I want to thank Genie for a great final, it was a really tough one."
"Hopefully I can come back next year!"
Earlier in the day, the unseeded pairing of Varatchaya Wongteanchai and Yang Zhaoxuan upset top seeds Liang Cheng and Wang Yafan, 4-6, 6-4, 10-7; for both winners, Sunday's win marks the first WTA title of any kind.
"In the first set we played well," Liang said after the match. "But didn't play our best game from the second set. I felt very sorry to my partner for my double fault in the end. But we'll move on and and continue to work hard."
All photos courtesy of BMW Malaysian Oepn 2016.