China fell behind 7-4 after the first three bouts, and world champion Li Na pulled it even at 9-9.
Sun won in a time of 14.31.02, eight and a half seconds ahead of his nearest rival and 3.12 seconds faster than the record he set in Shanghai in 2011.
Guatemala's Erick Barrondd claimed silver 1:18:57 and China's Wang Zhen took bronze in 1:19:25.
The world No. 2 seed duo breezed past the Japanese in the first game 21-10, before winning a hard battle in the second 25-23.
The fledgling Li was in very good form in the first game, dominating the court since the beginning.
China's mixed doubles players Zhang Nan and Zhao Yunlei beat their teammates Xu Chen and Ma Jin at the Wembley Arena Friday afternoon.
One day after China was stripped of the gold medal in the women's team sprint track cycling event, the cycling team announced on Friday that it would appeal.
Dong Dong of China scored 62.990 points to take the men's trampoline gold medal at the London Olympic Games on Friday.
China's Olympic badminton team will have the chance to silence their critics and offer some thrilling action on the court as they are guaranteed gold and silver in the mixed doubles.
China Railway Construction Corp. on Friday denied media reports that it had reached an agreement with Inter Milan to buy the Italian football club's 15-percent stake.
China will have to play medal-contender Brazil and host Britain in the remaining two group matches.
Table tennis "young guns" are getting a helping hand from more experienced "shooters" who know what its like to face an Olympic showdown.