BEIJING — Usain Bolt’s eyes darted to check the numbers on the trackside clock once, twice, three times, more.

For the only time in eight races at these Olympics, Bolt was really trying — gritting his teeth, pumping his arms, churning his golden spikes with those long, long legs. In the closing steps of the 200-meter final Wednesday night, with no other runner nearby, Bolt trained those mischief-loving eyes on the bright numbers he knew would ultimately define what already was a sublime performance.

And so he lunged at the finish. Yes, all alone out front, 25 feet clear of the nearest competitor, his second gold medal of the Beijing Games assured, the Jamaican dipped his head and thrust his 6-foot-5 frame through the last step of a sprint as special as the world has seen. Bolt leaned forward as if trying to edge an opponent who’d matched him stride for stride.

Just past the line, Bolt twisted his torso and turned his head around for one more glance at those numbers. Like everyone else who was watching, Bolt needed to be sure HE could believe what he saw.

The final tally on that clock was truly astounding. Bolt’s time of 19.30 seconds broke the world record of 19.32 set by Michael Johnson at the 1996 Atlanta Olympics, a world record that so many were so sure would last far longer than it did.

‘‘I just blew my mind,’’ Bolt said, ‘‘and blew the world’s mind.’’

He lifted his arms, then fell on his back, exhausted and exhilarated.

The milestone was magical.

The moment, too.

The medal? Consider this one of those once-in-a-generation instances at an Olympics where it was an afterthought, even if Bolt did put himself alongside U.S. swimmer Michael Phelps — the man with a record eight golds in Beijing — in forging one of the lasting memories from these Summer Games.

Even if Bolt is the first man since Carl Lewis in 1984 to win the 100 and 200 golds at a single Olympics, and the only man ever to do it by breaking world records in both.

‘‘I was, like, looking at myself,’’ Bolt said of checking out the overhead video scoreboards, ‘‘and I was like, ’That guy’s fast!’’’

The official results show that seven other men, including Shawn Crawford and Kim Collins, Walter Dix and Wallace Spearmon, were also competing this day, were also trodding that same Bird’s Nest track, were also running as hard as they could, nearly as fast as anyone ever has.

Crawford was the defending Olympic champion. Collins was the 2003 world champion. Dix won a bronze in the 100 behind Bolt on Saturday. Spearmon owns two world championship medals in the 200 and ranked as the fourth-fastest man in the distance’s history — yes, faster than Bolt’s previous best of 19.67 — until Wednesday.

No one provided a challenge.

Heck, no one finished within a half-second, an eternity in a race of this length.

And after two runners, Churandy Martina of Netherlands Antilles and Spearmon of the United States, were disqualified for running out of their lanes, the official results had silver medalist Crawford of the U.S. behind by 0.66 second — the biggest margin of victory in a 200 final at any Olympics. The DQs left Dix, another American, with bronze.

‘‘I’ve been dreaming of this since I was yea high,’’ Bolt said. ‘‘So it means a lot more to me actually than the 100 means.’’

Even before the race’s halfway point, when Bolt held a big lead that he was padding with each stride, it was quite clear that he really was racing against the men who long ago proved their excellence and set the sport’s standards.

Men such as Johnson. Or Lewis. Or Jesse Owens, who also pulled off the 100-200 double.

None of them was as tall as Bolt, who is turning what once was thought to be a liability in sprinting into an asset.

‘‘He got an incredible start. Guys of 6-5 should not be able to start like that,’’ Johnson said. ‘‘It’s that long, massive stride. He’s eating up so much more track than others. He came in focused, knowing he would likely win the gold — and he’s got the record.’’

That size is what the experts point to when asked how it is, exactly, that the man who calls himself ‘‘Lightning Bolt’’ could be so darn fast and could improve so, well, fast.

‘‘It’s his anatomy. He’s just blessed with an uncanny frame, an uncanny quickness, a huge competitive heart,’’ said Renaldo Nehemiah, the former world record-holding hurdler. ‘‘And he is having a good time, which I think our sport sorely needs to see: people enjoying themselves, having a good time. And he recognized the responsibility of seizing the moment — and he did it.’’

Said Crawford: ‘‘He’s revolutionized things.’’

Which is why Bolt found himself running against the clock, against those numbers that kept scrolling. After showboating his way to lowering his own world record to 9.69 in the 100 final — arms outstretched, slap to the chest — and taking it easy in heats for both of his individual events, he had vowed to finally push himself Wednesday.

‘‘I told myself, ’If I’m going to get this record, it’s going to be here, because the track is really fast,’’’ he said. ‘‘I told myself, ’I’m going to go out there and give it my all,’ and I went out there and just left everything on the track.’’

This time, he saved all of the emoting for after the race — blowing kisses to the fans, swaying his body to the reggae music on the stadium loudspeakers, walking barefoot around the track, putting his face inches from a TV camera, raising an index finger and yelling, ‘‘I am No. 1! I am No. 1!’’

As if anyone, track fan or not, anywhere in the world needed to be reminded.

Amid all of his pre- and postrace mugging and preening for the cameras, he repeatedly pointed to or popped out his yellow jersey with ‘‘Jamaica’’ written across the chest. That Caribbean island of 2.8 million is now 3-for-3 in the sprints at these Summer Games — Sherry-Ann Fraser won the women’s 100 Sunday — and collected another gold on the track with Melaine Walker’s victory in the women’s 400-meter hurdles Wednesday.

Bolt grew up in the same yam-farming Trelawny parish that Ben Johnson called home before moving to Canada. Johnson, as everyone knows, crossed the line ahead of Lewis in the 100 final at the 1988 Seoul Olympics in what would have been a world-record time of 9.79. But Johnson failed a drug test and was stripped of his gold medal and record.

There are sure to be cynics who will question Bolt’s emergence. He credits his improvement over the past few months — including first breaking the 100 record in May — to rededicating himself to training and made a point of partying less.

Before Wednesday’s race, track officials said Bolt had been drug-tested 11 times in 2008, including four since July 27. None has come back positive.

Shortly before the race, standing on the warmup track near the Bird’s Nest, Bolt unleashed a wide yawn, as though thinking, ‘‘Let’s get this thing started.’’

Wearing black track pants, a yellow T-shirt and the sort of regular sneakers you use to mow the lawn, he took a comfortable jog down a straightaway, putting forth about the same amount of effort he expended in the latter stages of the seven races he ran over the preceding five days.

He’ll be the first to tell you he isn’t big on taxing workouts. That, remember, is why Bolt persuaded his coach to let him add the 100 — and not the draining, full-lap 400 — to his specialty, the 200.

Hours later, as Wednesday melted into Thursday, which just so happens to be Bolt’s 22nd birthday, he wasn’t preparing to party.

No, the guy who rightfully can call himself the ‘‘World’s Fastest Man’’ and the ‘‘World’s Greatest Sprinter’’ had something else in mind, something he wanted to make sure he did before thinking one bit about chasing a third gold in the 400 relay final Friday.

Slowing down.

‘‘I’ve written history, pretty much,’’ Bolt said. ‘‘I just want to chill out. I just want to sleep. I wish I was in sandals right now.’’