American Aries Merritt ran a personal best of 12.92 seconds to win the Olympic men's 100m hurdles title Wednesday as the US closed in upon China on the medals table, courtesy victories in track and field.

Merritt got a flying start and held off the challenge of world champion Jason Richardson and Jamaica's Hansle Parchment to secure what in the end was a comfortable win. It is the first gold medal that the US have taken in the event since Allen Johnson took gold in Atlanta in 1996, Xinhua reported.

"I am so excited, words can't explain how excited I am right now," said Merritt. "People were talking about a world record, but 12.92 into a headwind is still pretty impressive. I am happy with that."

Richardson's silver gave the US an impressive 1-2 on a brilliant night for the Americans at the Olympic stadium, winning three of the four gold medals that were up for grabs.

Allyson Felix ended the disappointment of taking silver in the 2004 and 2008 Olympics by finally getting the better of Veronica Campbell Brown in the women's 200m final. The 26-year-old Felix was timed 21.88 seconds.

"To twice lose to the same person, it's been tough. But it's all paying off," said Felix. "I am so thankful to God for an amazing opportunity."

Britney Reese rounded off a wonderful night for the US when she won the women's long jump with a leap of 7.12 metres, while Natalya Antyukh of Russia completed a successful switch from the flat to hurdles with gold in the women's 400m final in 52.70 seconds.

Meanwhile, Jamaican superstar Usain Bolt cruised into the 200m final with a comfortable win.

He clocked 20.18 seconds, which was slower than his main rival, Yohan Blake, in the opening semifinal, but Bolt got off to an excellent start and ran a fast 100 metres to have the race under control before easing off in the closing straight.

"It's all about going as easy as possible, that was the aim. There's is no doubt who is going to come out on top, this is my favourite event and I'm looking forward to it. People always doubt the champion, but I don't have any doubts," Bolt said after his race.

The US captured its fourth gold on Day 12 through Misty May-Treanor and Kerri Walsh, who downed compatriots Jennifer Kessy and April Ross 21-16, 21-16 in the women's beach volleyball final for their third straight Olympic gold medal.

With just four days to go, China leads the gold medal count with 36, ahead of the Americans who had 34 gold. But the US have 81 medals overall, four more than China.

The Chinese paddlers eventually lived up to their expectations when Ma Long, Zhang Jike and Wang Hao had little problems against South Korea Wednesday in the men's team final, dropping just two sets en route to a comfortable 3-0 victory.

China's Wu Jingyu successfully retained her Olympic crown in the women's 49kg taekwondo when she overwhelmed three-time world champion Brigitte Yague of Spain 8-1 in the final.

"I was especially calm and relaxed in my matches today. Back in 2008 I wasn't so mature but in the past four years I have grown so much," said the 25-year-old Wu.

Joel Gonzalez made up for Yague's defeat by beating Lee Dae-Hoon in the men's 58kg class to hand Spain its first-ever Olympic taekwondo gold.

Elsewhere, Nathan Outteridge and Iain Jensen claimed a second sailing gold for Australia, winning the men's 49er at Weymouth.

In basketball, Russia defeated Lithuania 83-74 to reach the men's semifinals, where they face European champions Spain, who advanced by beating France 66-59.

In field hockey, reigning champions the Netherlands beat New Zealand after a penalty shoot-out to set up a final showdown against world champion Argentina, who upset host Britain in the other semifinal.