Updated

Athletics enters day two at the Summer Olympics on Saturday, with five medals decided in the evening session, but early on, all eyes were on the track for the round one heats of the men's 100 meters, one of marquee events of the entire Games.

With Olympic Stadium in a full roar, Jamaica's Usain Bolt won his heat in 10.09 seconds, a slow time for him, but he stumbled out of the blocks and then completely shut it down over the final 30 meters. It should be noted Bolt ran a 10.20 in the first round at Beijing. Fellow countrymen, and a couple of Bolt's biggest rivals for gold, Asafa Powell and Yohan Blake, both won their heats, too, finishing in 10.04 seconds and 10.00 seconds, respectively. All three qualified for the semifinals (Sunday, 2:45 p.m. ET).

Team USA is also sending three of its fastest runners to the semifinals: Justin Gatlin (9.97 seconds), Tyson Gay (10.08) and Ryan Bailey (9.88). Bailey's time set a new Olympic heat record for the U.S., breaking Gatlin's mark in the process, which had been established just eight minutes earlier.

The finals of the men's 100m is Sunday at 4:50 p.m. ET.