Usain Bolt will race the 200m final on Thursday after comfortably winning his semi-final, but there was no place for American rival Justin Gatlin as he failed to qualify.

Gatlin, who has served two doping bans, tied up late in his semi-final, blaming a stiff ankle as he finished third in 20.13sec to miss out on one of the eight final berths.

It was a different story for Bolt, however, who clocked a season's best of 19.78sec in the next step on his quest for an unprecedented sprint "triple triple".

Source: b'Source: PTI/File photo'

"I wasn't fully surprised," Bolt said of Gatlin's elimination.

"I thought he would have made it. But I could tell in the 100m he was feeling the pain and he was slowing down.

"It's just the fact you're getting old. To double at a championship where the young guys are stepping up is really hard."

Gatlin, who won 100m silver behind Bolt at the weekend, explained that he had not fully recovered from rolling his right ankle in late November.

"It's been flaring up this season. Tonight it got really stiff on me in the warm-up area and I wasn't able to properly warm up where I needed to warm up at," he said.

Source: b'Source: AFP/File photo'

"Having that lane three coming off the turn, I felt pain in the last 20 metres, I looked over and tried to hold on and do the best I could.

"I'm just glad I was able to walk off the track without a real harmful injury and be able to rest myself, get the treatment I need for my ankle and come out here and help my teammates in the 4x100m relay."

The towering Bolt eased up a full 40 metres from the line in his semi, to advance along with Canadian Andre De Grasse, setting a national record of 19.80sec as the second automatic qualifier.

"It means I'm definitely on the right track," Bolt said.

"I felt energetic and everything was going smooth. Hopefully I'll get a top lane tomorrow," he said, adding his preference would be lane six or seven where the bend is not perceived to be too sharp.

"It's always better for me because I'm taller."

Source: b'Source: Reuters'

World record a possibility 

Bolt added that he felt his own world record of 19.19sec, set when winning the 2009 world title in Berlin, could be under threat.

"I definitely think I can try for the world record, I definitely feel that," he said.

"But it's all about executing right, running the corner efficiently, then coming into the straight and just running the perfect race.

"I don't get over-confident, I'll come out and execute."