Usain Bolt (JAM) of Jamaica reacts after winning his race. [Photo/Agencies]

"I knew it was going to be hard to break the record because when I came off the corner my legs decided, 'now listen, we're not going to go any faster'.

"So I wasn't fully happy but I'm happy that I got the gold medal."

Bolt, who turns 30 on Sunday, confirmed this will be his last Olympics.

If he helps Jamaica win a third successive 4x100m relay on Friday to complete the triple-triple he will tie the record nine athletics golds won by Finn Paavo Nurmi, a 1920s middle and long distance runner, and American sprinter Carl Lewis.

Bolt said he would definitely run the 100 and relay at next year's world championships in London, though fears his coach might yet try to convince him to also go for the 200 title.