BERLIN — Usain Bolt burned up the track during today's 200-meter semifinals, looking set for an assault on a second world record at the world championships.

On the eve of his second medal race, Bolt thrived in 80-degree heat in Berlin, running hard before closing it down just past the halfway mark and strolling past the line in 20.08 seconds.

If he had pushed, Bolt could easily have broken Tyson Gay's 2007 championship record of 19.76 seconds. Bolt's world record stands at 19.30.

Defending champion Gay is injured and out of the 200, and American teammate Shawn Crawford had to push hard to qualify third in Bolt's heat.

In the second semifinal heat, American sprinter Wallace Spearmon finished first in 20.14, edging Steve Mullings of Jamaica.

The temperature is expected to exceed 85 degrees Thursday at the Olympic Stadium, and Bolt loves the heat.

He cut through the swelter of Beijing last year on his way to three Olympic golds and as many world records.

Bolt will be looking to give his Caribbean nation a 3-0 edge over the United States in sprint events, bringing Jamaica closer to the 5-0 thrashing of Beijing.

Defending women's 200 champion Allyson Felix will try to lift the gloom hanging over the American sprint team when she enters qualifying for the 200. But much like the American runners facing Bolt, Felix will have to battle the surging Jamaican women sprinters.

After being the star with three golds at the last world championships in Osaka, Japan, Felix was upstaged at the Beijing Olympics in the 200 by Veronica Campbell-Brown.

The United States will also be looking for gold in the 100 hurdles, with Olympic champion Dawn Harper and teammate Damu Cherry favored to medal, and in the men's 1,500, where defending champion Bernard Lagat is set to race later Wednesday.

So far, the Americans have three golds and seven medals overall, ahead of Russia with two golds and seven total. Jamaica has two golds and five medals overall.

Olympic champion LaShawn Merritt and defending champion Jeremy Wariner left little doubt the U.S. could count on another gold in Friday's 400 final, firing each other up for another battle for one-lap supremacy.

Wariner had dominated the distance since the Athens Games in 2004, but Merritt upset him at the Beijing Games last year to take Olympic gold.

Merritt looked at the stadium clock to make sure of winning his semifinal heat and still set a world leading time of 44.37 seconds. Wariner coasted to a 44.69.

What looked like a guaranteed gold for Cuba with Dayron Robles in the 110 hurdles suddenly looked shaky when the Olympic champion hit the first obstacle and struggled to get to the semifinals with the slowest qualifying time.