LONDON — Usain Bolt is an all-but-impossible track and field act to follow.

So on Thursday night, with the stadium full and the London weather just right, David Rudisha took full advantage of performing first.

There were no pacemakers in this Olympic 800-meter race, so Rudisha, the Kenyan star, set his own torrid pace: 49.28 seconds for 400 meters, 1 minute 14.30 seconds for 600, with the stadium announcer’s voice rising with anticipation. And in the final curve and final straightaway, Rudisha finished the job, along with his own world record, crossing the line with his wide eyes fixed firmly on the digital clock as it flashed “1:40.91.”

“Nobody has done the world record in the 800 without pace setting,” Rudisha said. “I thought it was going to be difficult. I knew I could run 1:41, but breaking the world record was a different story. But I was very determined, and I knew I was in good shape this year.”

With the crowd and the wider world bracing for something extraordinary from Bolt in an hour or so, Rudisha had beaten him to it, but Bolt did not fade quietly into the night.