London, Aug 6 (IANS): Usain Bolt won Olympic gold in the men's 100 metres Sunday, screaming to the line in an Olympic record of 9.63 seconds.

The Jamaican collected his fourth career Olympic gold ahead of world champion teammate Yohan Blake, who clocked 9.75 for silver, with 2004 champion Justin Gatlin taking the bronze in 9.79 seconds.

"I knew it was going to be like this," Bolt said with typical self-assuredness.

Bolt's world record of 9.58 seconds, posted in 2009, remained intact, but it was still the second-fastest 100 metres time of all time.

The 25-year-old got off to a customary poor start, but switched gear at 50 metres to storm past Gatlin and Blake and across the line.

"I was slightly worried about my start, I slipped a little in the blocks. I don't have the best reactions, but I secured it and that's the key," said Bolt.

"My coach told me to stop worrying about the start and concentrate on the end because that's my best."

Bolt adds the title to the 100 metres, the 200 metres, and the 4x100 metres relay gold medals that he won in Beijing.

The 2007 world champion Tyson Gay came fourth with 9.80.