Carl Lewis v Ben Johnson on the track, the United States v Australia in the pool, India v Pakistan on the hockey field -- all classic head-to-head Olympic rivalries that live long in the memories of fans.

Throughout the 28 sports of the Games, long-standing conflicts are settled on the biggest stage of all and no world title or record can match the glory of Olympic gold.

Athens is sure to produce its own unforgettable clashes and, as always, the men's 100 metres is among the most eagerly-awaited showdowns.

The main rivalry in the blue riband event is a relatively new one, between Olympic champion Maurice Greene and Jamaican Asafa Powell.

Powell beat the American twice in the build-up to the Games to become a real threat to Greene's hopes of winning back-to-back gold on the track.

"I think he's a good athlete," says Greene, who feels he has deserved the title of the world's greatest-ever sprinter. "Do I think he's better than me? No."

Only Lewis has won consecutive 100 metres titles but his second gold, in 1988, came after he crossed the line second behind Johnson, who was subsequently disqualified for doping.

There is also a fantastic race in store in the men's 10,000 metres, though it will have to be something special to top the 2000 edition when Haile Gebrselassie caught his longstanding rival Paul Tergat right on the line to repeat the 1-2 of Atlanta.

YOUNGER THREAT

Tergat is racing the marathon this year but Gebrselassie has a new, younger threat in the shape of fellow Ethiopian Kenenisa Bekele.

The 22-year-old has taken his compatriot's 5,000 and 10,000 metres world records this year and will be bidding to spoil Gebrselassie's bid for an unprecedented third successive 10,000 metres gold.

The women's pole vault has seen a terrific all-Russian rivalry over the past year with Yelena Isinbayeva and Svetlana Feofanova setting eight world records between them. The two are both competing in Athens where Isinbayeva's two-week old mark of 4.90 metres could go.

Olympic swimming has long been something of a battle between the sport's superpowers of Australia and the United States and each country has a man bidding for a special place in Games history.

American Michael Phelps is trying to win an unprecedented eight gold medals while Australia's Ian Thorpe is looking to add another six to the three he won in Sydney.

The pair will clash in three relays and go head to head in the 200 metres freestyle, which promises to be the highlight of the swimming programme.

India and Pakistan were fierce rivals as they vied for Olympic men's hockey supremacy from 1948 to 1984, although they have both fallen off the international pace somewhat since Pakistan won gold in Los Angeles.

MUTUAL BOYCOTT

This year they have been kept apart in the group stage but could meet in the semi-finals, a game that would be huge for both countries who are only just thawing a five-year mutual sporting boycott.

In the equestrianism three-day event, one of the few Olympic sports where men and women compete against each other, there is a very special rivalry as Australian Andrew Hoy will be up against his wife Bettina, who is competing for Germany - riding an Australian horse.

Mrs Hoy, who won a bronze with West Germany in 1984 when she was known as Bettina Overesch, says there is no problem with the situation as she seeks to prevent her husband winning a record fourth successive team gold.

"We both want to win but we are delighted for each other's competitive success. We support each other every chance we can," she said.

There is a family connection in fencing too where 1999 world sabre champion Damian Touya of France is seeded to face his elder brother Gael in the semi-finals.

Another local fencing rivalry has gone global where two women from the same Italian town of Jesi go point to point in the foil.

Four years ago Valentina Vezzali and Giovanna Trillini took gold and bronze respectively and the two are back for more.