"I've had so much success in Asia," Williams said after the match, having won her last two titles at the Dongfeng Motor Wuhan Open and the Huajin Securities WTA Elite Trophy Zhuhai. "I feel like it's very lucky to play here."
The American appeared to have things under control from the outset, but Doi, who held a match point against eventual Australian Open champion Angelique Kerber in their Melbourne first round, rebounded in style to win four straight games and lead Williams by a break.
"My opponent was incredible today. I was leading in the first set and then suddenly she was leading!"
That proved to be the last major momentum swing, however, as the former No.1 swept the final three games to take the first set and drop just two more to win the final in just under 90 minutes.
"It's fun to win a final that was such a challenge, and I appreciated her game."
Williams didn't lose a set through five matches in Kaohsiung, and will hold on to her current ranking of No.11 by virtue of winning the title. A fan favorite in Taiwan, she was happy to be celebrating Valentine's Day at a tournament where she could truly feel the love.
"Of course, I celebrated Valentine's Day with a win; that's the best way! I made so many wonderful moments and memories that I'll be bringing a lot of love back with me to the States.
"The last five days were so exciting, just to feel the enthusiasm and to play great tennis every day. It was perfect week for me and the tournament did an amazing job with everything; the players and fans felt so welcome, so it was perfect."
Doi had come into the match hoping to win her second career titles - having won her first last fall at the BGL BNP Luxembourg Open - but nonetheless finds herself just outside the Top 50 thanks to her run in Taiwan.
In doubles, hometown favorites Chan Yung-Jan and Chan Hao-Ching won their first title of 2016, defeating Japanese duo Eri Hozumi and Miyu Kato, 6-4, 6-3. The Chan sisters roared into the BNP Paribas WTA Finals Singapore presented by SC Global last year as Martina Hingis and Sania Mirza's closest competitors, and remain the last team to defeat Santina, who currently ride a 40-match winning streak - the longest since 1990 (Jana Novotna, Helena Sukova).
The Chan sisters pledged to donate all of their $17,700 prize money to Taiwan's earthquake relief effort. The 6.5 magnitude earthquake that struck southern Taiwan on February 6 has claimed 116 lives, recent reports have stated.
"Because of the devastating earthquake in Taiwan a week ago, we've decided to donate our prize money from this tournament to Tainan to support them," Chan Yung-Jan wrote on her Facebook page. "We had a similar experience before, so it's time for us to give something back."