Rio de Janeiro, Aug 18 (IANS): Jamaican sprinter Usain Bolt admitted he will need to improve himself in order to break the world record in Thursday's 200m final at the Rio Olympics.

The seven-time Olympic champion qualified fastest in 19.78 seconds to edge out Canadian Andre de Grasse by two hundredths of a second on Wednesday, Xinhua news agency reported.

Lashawn Merritt of the US was third quickest at 19.94 seconds.

"I definitely think I can try for the world record, I definitely feel that. I need to run efficiently and get into the straight and run the perfect race," Bolt said.

"If I can run a little more efficiently on the turns. I will be hoping for lane six or seven maybe to be able to run as smooth as I can. My body felt good. It is tougher than I thought it was going to be but I am handling everything pretty well mentally and physically," he said.

Bolt looked to be cruising to an easy win in his semifinal before being pushed at the end by De Grasse.

The 29-year-old was mildly miffed at his rival, questioning the need to exert himself.

"That was really unnecessary. I don't know what he was trying to do but he is a young kid, he is great," Bolt said.

"He was supposed to slow down. I said 'What are you doing, it's a semifinal,' But I think he wanted to push me. I was a bit lazy but I got round," Bolt added.

Surprisingly, American Justin Gatlin failed to qualify for the final, finishing ninth fastest in the semifinals at 20.13.

Bolt became the first man to win three straight Olympic 100m titles on Sunday by beating Gatlin by eight hundredths of a second, with De Grasse taking bronze.

Already considered the most successful sprinter of all time, Bolt is hoping to achieve an unprecedented triple-triple here: three straight Olympic gold medals in the 100m, 200m and 4x100m relay.