Usain Bolt enlarged his legend Saturday night with some good, old-fashioned work. For the first time this week, he crossed the finish line with the look of a straining, hard-driving sportsman rather than a triumphant showman. He even threw his chest forward and leaned.

There was no doubt in Olympic Stadium that Bolt would get his third gold medal of these Summer Games when he got the baton in the 4x100-meter men’s relay final about even with American anchor Ryan Bailey.

Bolt’s challenge in the homestretch was getting the world record — just about the only distinction he hadn’t earned, or proclaimed himself deserving of, this week.

With a furious run through the line that left Bailey looking overmatched, Bolt strode home in 36.84 seconds, knocking 0.20 off the world mark he and his Jamaican teammates set at the 2008 Summer Games. And he did it without striking a single pose.

“I was smiling after the race,” Bolt said. “I was running really hard. I was really focused on running as fast as possible, because we really wanted the world record. . . . The fans were happy about the world record, so they forgave me for that.”

Bolt also said: “It’s just a wonderful end to a wonderful week.”

The U.S. team of Trell Kimmons, Justin Gatlin, Tyson Gay and Bailey could take consolation in this: Their silver-medal finish in 37.04 broke the American record for the second straight night and matched Jamaica’s previous world mark.

“We broke our American record twice,” said Gatlin, who ran the second leg of Saturday’s squad and anchored the U.S. team that broke the 19-year-old mark in the heats Friday. “That record was standing for 20 years before we touched down in London . . . I think it showed that America is getting ourselves together . . . We’re back.”

Earlier, the U.S. women had offered up a brilliant race of their own, winning the 4x400 relay gold with the fourth-best time ever and the fastest since the 1988 Summer Games in Seoul.

Their finish in 3 minutes 16.87 seconds also was the second-fastest run by a U.S. team, trailing only the 3:15.51 posted by a 1988 squad anchored by Florence Griffith-Joyner at the Seoul Summer Games, when the Soviet Union set the current mark of 3:15.15.

“I kind of felt like I was on a victory lap because they gave me such a big lead,” said Sanya Richards-Ross, the Olympic 400 champion who ran the anchor leg. “To be able to prance around the track one more time . . . it’s a great feeling.”

American Brigetta Barrett, 21, added a silver in the high jump on the last night of competition. That gave the U.S. track and field team 29 medals, well ahead of second-place Russia, which has 18, with the hope of adding one more in Sunday’s marathon. If Ryan Hall, Meb Keflezighi or Abdi A bdirahman comes through in that event, that would give the U.S. team the 30 it sought after a miserable Summer Games in Beijing.

Though the United States won a respectable 23 track and field medals to lead the medal table in Beijing, it concluded those Olympics with stunning, back-to-back baton drops in the 4x100 relays that led to an overhaul of the team’s performance division and the elimination of USA Track and Field’s six-year-old relay program.

U.S. men’s Olympic track coach Andrew Valmon said the U.S. coaching staff sought changes in spirit more than technique at these Games.

“We asked everyone to check their egos at the door, and we talked about country and team,” said Valmon, the University of Maryland’s track and field coach. “Ultimately, we’re excited about where we are.”

This year, the U.S. relay teams produced no bobbles and mostly excellence, even though the U.S. men won silvers in both events. The men’s 4x400 team was hampered by injuries to three of its top six athletes, including the 2008 Olympic 400 gold and silver medalists, and the 4x100 relay team simply met a better match in a Jamaican team anchored by the fastest man in history.

On Friday, the U.S. women’s 4x100 relay team shattered a 27-year-old world record in winning gold. Saturday, the women’s 4x400 relay team beat second-place Russia by 3.36 seconds.

Saturday’s relay highlight came from Allyson Felix, who became the first U.S. woman since Griffith-Joyner in 1988 to win three gold medals in one Games. She also ran the fastest leg of the night: 47.8 seconds. That topped the 49.10 run by Richards, who won the gold in the 400 earlier in the week.

“I considered us to be the Dream Team of the 400,” said DeeDee Trotter, who ran the leadoff leg. “We were definitely gunning for the world record. You can believe that. We wanted to get it and it’s definitely on my checklist of things to do.”

The British crowd might argue the night belonged to Britain’s Mo Farah, who became the seventh man to win golds in the 5,000 and 10,000 in the same Games with his 5,000 victory in 13 minutes 41.86 seconds. But for nearly everyone else, the Olympic Stadium was Bolt’s stage.

As usual, that was particularly the case for Bolt, who two days after declaring himself a living legend served up some heavy showboating during his victory lap. He even paused to pose with Farah, putting his hands above his head in Farah’s trademark “M” as Farah did Bolt’s signature pose.

The victory gave Bolt six gold medals in his Olympic career: the 100, 200 and 4x100 golds in the last two Summer Games. Earlier, International Olympic Committee President Jacques Rogge had said Bolt would not be a legend until he returned for multiple Olympic Games. Bolt said he hoped to be back for the 2016 Games in Rio de Janeiro, but made it clear he didn’t think he needed to return.

“Next time you see him, I think you should ask him what Usain needs to do that no human has ever done,” Bolt said. “Because I’ve done it already.”