Jankovic's win gave the 30-year-old her 14th WTA career title and her first since she won on clay in Colombia in 2013, although she did win a lower tier event in China in August.
"It's amazing to win a title in China for the second time this year -- obviously China is very special to me!" she told the crowd.
Jankovic also heaped praise on Allertova, who was playing in her first WTA event final and had claimed the scalps of world number two Simona Halep and third seed Sara Errani in getting to the decider.
"Denisa, you had such a great run here in Guangzhou, beating such great players," Jankovic said. "And you played so well in the final -- it was definitely closer than the result says.
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"You'll have many more finals and many more titles in the future, so just keep going, just keep doing what you're doing."
Allertova made a promising start to the final, recovering from a sloppy opening service game, but it was all one-way traffic after that.
"It was an amazing time for me here," Allertova said.
"I'm so happy I could beat so many good players here and play my first final. Jelena was too good, but I'm happy with my week."
(Reporting by Julian Linden in Singapore; editing by Sudipto Ganguly)
