FACTBOX: Ten great rivalries at Beijing

(Reuters) - Following are 10 sporting rivalries worth watching at the Beijing Games, starting on Friday:

1) JEREMY WARINER V LASHAWN ,MERRITT, 400 METRES

Olympic and world champion Wariner has dominated the 400 meters since before the 2004 Games. Compatriot Merritt has been in his slipstream throughout and is getting closer. Wariner remains favorite to retain his title but things have certainly got closer since Merritt bet him twice earlier in the season. The second of those victories came in the U.S. trials when he said afterwards: "Once I got into the home stretch I was smelling Beijing and victory." Only Michael Johnson, something of a mentor for Wariner, and Butch Reynolds have run faster than Wariner's best time of 43.45.

2) KENENISA BEKELE v HAILE GEBRSELASSIE, 10,000 METRES

The winners of the last three Olympic 10,000 meters titles go head-to-head with Ethiopia's Gebrselassie hoping to roll back the years for a sign-off triumph over his compatriot. Gebrselassie won gold in 1996 and 2000, both times beating Kenyan Paul Tergat in terrific races. As world record holder and four-times world champion he was the undisputed 10,000 king before moving on to the marathon.

Bekele took the older man's world records at 5,000 and 10,000 meters, succeeding him as Olympic champion and notching up three world titles. Gebrselassie, now 35, nine years older than Bekele, opted out of the Beijing marathon because of concerns over the air quality.

3) MICHAEL PHELPS v MARK SPITZ, SWIMMING

Phelps, born after his fellow American retired, is engaged in a battle with Spitz for the title of the greatest swimmer of all time. Spitz has held that mantle since he won seven gold medals, all in world record time, at the 1972 Munich Olympics. Phelps came close to matching his mark at Athens four years ago when he collected six golds but is chasing eight in Beijing. Phelps is due to swim the 200 and 400 meters individual medley, the 100 and 200 butterfly, the 200 freestyle and three relays in Beijing -- and is favorite to win all of them. Australian head coach Alan Thompson says the American is more than capable of the record feat but his team mates Ian Crocker and Ryan Lochte could spoil the party.

4) KATIE HOFF v STEPHANIE RICE

American Katie Hoff and Australia's Stephanie Rice will clash in women's individual medleys. Hoff won both events at last year's world championships before teenager Rice threw down the challenge when she broke the world records for both events at this year's Australian Olympic trials. Hoff regained her record in the 400 during the U.S. trials. Rice was romantically linked with Eamon Sullivan but they called off their relationship just before the Beijing Games. Sullivan broke Alexander Popov's world record for 50 meters this year but lost it to Bernard a few months later before regaining it at the Australian trials.

5) ISABELL WERTH V ANKY VAN GRUNSVEN, EQUESTRIANISM

Dutchwoman Van Grunsven has stopped giving interviews so she can throw everything into beating her equestrian dressage rival of the past two decades, Germany's Werth, and winning her third successive Olympic gold. She clinched her ninth World Cup title this year by beating Werth, who won silver in Barcelona and then captured the gold medal at the 1996 Atlanta Games by edging out the Dutchwoman. Werth also won silver in 2000. Beijing is almost certainly the sixth and last Olympics for van Grunsven because her children are more important to her than a gold nowadays.

6) YANG WEI V THE HORIZONTAL BAR, GYMNASTICS

With no Paul Hamm in the field, the only obstacle standing in Yang's way to winning the Olympic all-round title is likely to be the horizontal bar. Four years ago the Chinese favorite was leading the competition going into the final rotation but his Olympic dreams came crashing down when he lost his grip on the bar and finished out of the medals. At the 2007 world championships, Yang again failed to master his hold on the apparatus and suffered a crashed landing. This time, such was the lead he had built up over his rivals, the fall could not deny him a place on the top of the podium.

7) CHINA V U.S. WOMEN'S TEAMS, GYMNASTICS

China reigned supreme at the 2006 world championships before being dethroned 12 months later by the United States, who won their first world team title on foreign soil in Stuttgart. The Americans will be relying on the dynamic skills of Shawn Johnson and the artistry of Nastia Liukin while the Chinese have a team packed with specialists led by vault and floor supremo Cheng Fei, fourth in the 2004 Olympics in the floor. Carly Patterson of the U.S. won the individual all-round in Athens in 2004 and the American team were second behind Romania in the team competition.