The 33-year-old, who led home a clean Kenyan podium sweep in the event in Daegu 2011, made history as the first woman ever to land back-to-back marathon titles in World Championships
Up against a hot and humid temperatures over 28 degrees Celsius, the Kenyan reigning World champion overcame a neck-and-neck battle with Italian national record holder Valeria Straneo with 2 km left, bursting ahead to finish with a time of 2:25:44 hours.
The Italian Straneo, 37, took the lead as soon as the runners left the Big Sports Arena and held on till the 40km mark. She ran 5 km in 17:05, 10 km - in 34:12. 20 km - in 1:09:02. She clocked 1:12:58 for the half-marathon, 1:26:36 for 25 km, 1:44:00 for 30 km and 2:01:15 for 35 km.
Straneo, who was 7th at the London 2012 Olympics, unexpectedly finished with the silver clocking 2:25:58 with Kayoko Fukushi from Japan third in 2:27:45.
With the exception of Kiplagat, there were no Kenyans and Ethiopians in the top-10.
"I am delighted I was able to defend my title successfully," said Kiplagat.
"The time of the race is unusual, because I am used to run most of my races in the morning. So during my preparation I tried to adjust my training to the time.
"I got confident I was going to win at 40km, when I started to increase my pace. I dedicate my victory to my husband for letting me have enough time to train," she added.
Jeilan lost to Farah
Ethiopian Ibrahim Jeilan lost his World title in the men's 10,000m to the reigning Olympic Champion, Mohammed Farah of Great Britain.
The Somalia-born Briton increased the pace drastically over the last two laps and managed to hold off Jeilan in the home straight to win gold in a season's best time of 27:21.71.
Jeilan settled for the silver medal in a season's best time of 27:22.23 while Kenyan youngster Paul Tanui took the bronse medal in 27:22.61.
"I'm happy with my silver medal," says Jeilan. "My preparation for the World Championships was the same as two years ago."
"But with 2 weeks to go until the race I got ill and had to miss three days of training, basically two main training sessions. I believe that's why I lost gold. I don't do any special preparation for the finishing spurt, but I have the speed for it.
"I enjoyed my first time in Russia, it is an interesting country, and everything was just perfect - the food, the hotel, the transportation, the conditions".
On his part, Paul Tanui said: "It is a great happiness that I feel inside of me. I have never performed like this before. It was a tough race.
"I have never run a tough race like this. I am very satisfied with my performance. Never before have I had a medal. I congratulate myself. I am full of happiness."
Kenya dominated the women's 3000m steeplechase qualifying races with Milcah Chemos Cheywa and Hyvin Kiyeng Jepkemoi clocking 9:36.16 and 9:36.19 respectively.