Justin Gatlin hit back at US swimmer Lilly King after breezing through his opening 100m heat to remain on an Olympic collision course with Usain Bolt.

Teenage star King made headlines this week when she said athletes like teammate Gatlin who had previously failed dope tests should be barred from the Olympics.

But Gatlin, 34, who has twice been convicted of doping offences, gave King's comments short shrift after coasting through his opening heat in 10.01 sec.

"I don't even know who Lilly King is - she does swimming, not track and field. I'm not worried about that," Gatlin said.


"I've come back and done what I need to do. I work hard like everyone else does and I've gotten tested just like everyone else has."

Gatlin, the 2004 Olympic champion, insists that his role as the pantomime villain of athletics is wide of the mark, adamant that he has paid his dues after serving a four-year ban for the second of his two doping offences.

"I have confidence in the policies. USADA (United States Anti Doping Agency) has done a great job, WADA (World Anti-Doping Agency) has done a great job," he said.

"I've come back and done what I need to do. I've worked hard to get back to here, I've been tested like everyone else and I believe in the system like everyone else."

Gatlin's time was the fastest of the morning, with Jamaica's defending champion Bolt fourth quickest after clocking 10.07 sec in warm sunny conditions.

The 30-year-old world record holder, greeted with acclaim by the large crowd, will also bid to defend his 200m and 4x100m relay golds for the third time later in the week.

"It wasn't the best start. I felt kind of slow. I'm not used to running this early at any championship," said Bolt.

"I'm feeling good. I'm happy. As I said, I've got the first one out of the way so I'm happy about that. So now it's all about execution and getting it right when it comes to the finals," added Bolt, predicting a fast semi-final.

"It's definitely going to be a good semi-final. There are a lot of guys running fast. It's good. It gets you running and gets you up to speed to go out there in the finals."

The second fastest time of the morning session was posted by the Ivory Coast's Ben Youssef Meite, with 10.03 sec.

Canada's Andre De Grasse also impressed, the 21-year-old posting 10.04 sec. Chinese sprinter Xie Zhenye was fifth fastest, winning his heat in 10.08.

The semi-finals of the 100m take place on Sunday with the final scheduled for 10.25 local time (11:25am EST).