Compatriot Bo Van Pelt, who won in Malaysia last week, posted a 67 to take a share of second place alongside Sweden's Fredrik Jacobson and Alexander Noren at the Sheshan International Golf Club.
Asian Tour stalwarts Thongchai Jaidee of Thailand and Korea's K.J.Choi carded matching 68s to take tied-fifth place together with American David Toms and England's Justin Rose.
A graduate of the Nationwide Tour, Bradley won his first Major at the PGA Championship in August. The PGA Tour rookie continued to serve notice of his talent by beating the season's other Major winners to lift the PGA Grand Slam last month.
After his commanding start at the Sheshan International Golf Club, Bradley is now beginning to live out his dream.
"A year ago this week, I had just got my PGA Tour card from Daniel Island. It was probably the happiest, most fun week of my entire life. It was the realisation of a dream," said the 25-year-old American.
"I feel like I have to pinch myself out here, because of what's going on and just how much fun I'm having doing it. And to think a year ago, I would be sitting here, taking the lead is pretty remarkable," added Bradley.
Playing alongside England's Lee Westwood and Australian Adam Scott, Bradley marked his flawless card with five birdies and an eagle to upstage his illustrious playing partners.
"I'm amazed at who I'm around. And to be in a group like that in this tournament and to play like that on this course, is very rewarding and it means a lot to me," said Bradley.
"I'm just very proud of the way I played, and it's just a very rewarding round," added the American.
Bo, who bagged his career's biggest pay cheque with his second PGA Tour win in Malaysia last week, is hoping to end his season on a high.
Bo mixed seven birdies against two bogeys to continue his good form but knows that he has to stay focused for the rest of the week.
"This'll probably be my last tournament of the year so I want to end it on a high. The two times I've won professionally, I haven't played well the following week, so obviously I'm concentrating today [Thursday] and trying to keep it up," said Bo.
Leading scores after round 1 of the HSBC Champions 2011 being played at the par 72, 7266 Yards Sheshan GC course (a- denotes amateur):
65 - Keegan BRADLEY (USA).
67 - Fredrik JACOBSON (SWE), Bo VAN PELT (USA), Alexander NOREN (SWE).
68 - Thongchai JAIDEE (THA), K.J. CHOI (KOR), David TOMS (USA), Justin ROSE (ENG).
69 - Aaron BADDELEY (AUS), Peter HANSON (SWE), Lee WESTWOOD (ENG), Adam SCOTT (AUS), Simon DYSON (ENG), Rory SABBATINI (RSA), Graeme MCDOWELL (NIR), Jhonattan VEGAS (VEN), Martin KAYMER (GER).
70 - Rory MCILROY (NIR), Charl SCHWARTZEL (RSA), Jbe KRUGER (RSA),