The 23-year-old Serb also won the China Open last week and the Italian Open earlier this year.
"I am really proud of myself,'' she said. "I am playing with a lot of confidence and I played some good tennis this week.''
Jankovic was assured of taking over the top ranking Monday regardless of the outcome of the final. She already held the No. 1 spot for one week in August.
"I feel that every day I am getting better and better. I am really working on my game, I want to reach my full potential,'' she said.
Serena Williams became the No. 1 after beating Jankovic in the final of the U.S. Open, but the American will drop in the rankings after losing her opening match in Stuttgart.
Jankovic is signed up for next week's Kremlin Cup, although she left open whether she would actually show up in Moscow for the tournament, which Williams is skipping.
"I feel tired now, but mentally I am not tired, I am hungry to do well. I want to finish the year as No. 1,'' she said.
Jankovic won her eighth career title after overcoming a brief lapse in the second set against the 18th-ranked Russian, who won the Stuttgart tournament in 2006.
After the win, Jankovic took a spin in the red Porsche 911 convertible given to the winner and appeared to have more trouble controlling the powerful car than the match.
She broke serve in the opening game and that was enough to give her the set against an error-prone Petrova.
"I really wanted to win this trophy and when you want too much sometimes it doesn't work in tennis,'' Petrova said. "I gave it my best.''
Jankovic also broke to start the second set, but Petrova broke back to tie it at 3-3. The Russian was unable to keep the momentum, however, and dropped serve again after a series of errors. Jankovic won the match when Petrova put a forehand long.
"I got a bit flat in the middle of the second set, I had some tough matches behind me and I was getting tired,'' Jankovic said. "I tried to stay positive, to be aggressive and to switch into a higher gear, it was an important game.
Petrova had not dropped a set this week until the final. Jankovic has been playing with a painful left foot after tearing off a toe nail. She needed painkiller shots before her semifinal win over Venus Williams and got two more before the final.
Asked about her foot at the post-match news conference, Jankovic misunderstood the question and replied, "The food is great.''
Realizing the mistake, Jankovic burst out laughing and then added:
"It's numb during the match and I don't feel anything, but after a couple of hours it hurts a lot,'' she said. "The doctor told me to wear flip-flops but I am flying to Serbia tonight, I can't go in flip-flops like I am going to the beach.''
Jankovic tops Venus to reach Porsche final
Petrova reaches Porsche GP final
Forlán Returns To Recover In Madrid
Sporting Injury Worries Lessen
