LaShawn Merritt of USA celebrates New Junior World Record in the 4x100m Relay Final (© Getty Images)
GrossetoThree brilliant World record relay performances by United States' athletes, were the highlight of the closing day of the World Junior Championships in Grosseto on Sunday.
The outstanding overall table-toppers at these Championships, achieved a clean sweep of all four competitions and set World Junior men's 4x100m and 4x400m plus the Junior women's 4x400m records.
The men after narrowly missing their own World 4x100m relay record by only 0.04sec in the semi-finals, came up trumps in the final.
Slick baton changing at every changeover saw the foursome of David Kimmons, Demi Omole, Ivory Williams and LaShawn Merritt, roar to a new world record time of 38.66sec.
That was 0.26sec quicker than the 38.92sec which won them the title two years ago, and well clear of the opposition.
Jamaica and Japan both achieved season's bests of 39.27sec and 39.43sec for the silver and bronze medals, but were never in contention.
The feat was matched by their women who less than 20 minutes later shattered the 16-year-old 4x400m record set by the former German Democratic Republic in Sudbury.
Alexandria Anderson crashed to the ground exhausted after a superfast first leg, and was receiving treatment as her colleague's Ashlee Kidd, Stephanie Smith and Natasha Hastings roared to a time of 3min 27.60sec.
Winning well clear of Russia who set a National record of 3min 30.,03sec and Jamaica (3min 30.37sec), the USA easily bettered the previous mark of 3min 28.39sec.
Then in the last event of the Championships, the USA's quartet of Brandon Johnson, LaShawn Merrit, Jason Craig and Kerron Clement lowered the 4x400m mark which was set by their much earlier colleagues in 1986.
The inaugural Championships in Athens, saw the USA storm to a time of 3min 01.90sec. Today it was reduced by 0.81sec by their successors.
South Africa and Japan won the silver and bronze medals with African and Asian area records of 3min 04.50sec and 3min 05.33sec.
Jamaica with some slick baton changing looked set to retain their women's 4x100m relay crown, until Shalonda Solomon produced a storming last leg for the United States.
The 200m gold medallist taking the baton from Jasmine Baldwin, flew down the finishing straight anchoring her side to its first victory in the event for six years.
The American's time of 43.49sec was the fastest in the World this year. Jamaica (43.63sec), clocked its quickest of the summer while France, the bronze medallists, set a National record of 43.68sec.
Iran claimed its first-ever World Junior Championships medal - it was fitting Ehsan Hadadi collected a golden one with his discus victory.
Hadadi despatched his implement 62.14m to win ahead of Russia's Oleg Pirog who had a personal best throw of 60.28m with Serbia and Montenegro's Luka Rujevic third with a 59.82m effort.
Augustine Choge became the sixth Kenyan to win the 5000m gold medal at these 10th Championships,his break 200 metres from home destroying the challenges of Ethiopian's Bado Worku and Tariku Bekele.
Choge won in his fastest time of the summer: 13min 28.93sec, with Worku claiming a personal best in 13min 30.45sec.
In his slipstream, Bekele the younger brother of World 5000m and 10,000m record holder Kenenisa, took the bronze medal, clocking 13min 30.86sec.
Aries Merritt won the opening track event of the day when retaining the 110m metres hurdles for the United States.
The World's second fastest junior this summer, won in an untroubled time of 13.56 seconds ahead of Dayon Robles.
The Cuban prevented a US one-two, although he and Kevin Craddock shared the same mark of 13.77sec in a tight finish.
Nelya Neporadna last years European champion controlled the 1500 metres final with a fist of steel, from start to finish.
After a fast first lap of 66.79sec, the Ukrainian slowed the pace considerably, before unleashing an unstoppable burst for the line over the last half lap.
Neporadna claimed victory in 4min 15.90sec ahead of Russia's Anna Alminova with Siham Hilali of Morocco, third in 4min 17.39sec.
Irina Kovalenko increased her own world leader of the year when achieving her best ever performance by a centimetre, to win the high jump with a clearance of 1.93m.
The silver went on countback to Russia's Svetlana Shkolina ahead of America's Sharon Day both achieving personal bests of 1.91m.
Godfrey Mokoena - unlucky not to win the long jump - claimed a second victory for South Africa at the Championships, winning the triple jump with a clearance of 16.77m.
China's Zhu Shujing fiished runner-up wsith a best leap of 16.64m while a Ukrainian record of 16.58m won the bronze medal for Viktor Kutnetsov.