London - Hopes of continuing South Africa's medal momentum were shattered on Friday, the first day of the track and field events, when both Cornel Fredericks and world bronze medallist LJ van Zyl were eliminated from the 400m hurdles competition at the London Olympic Games.

Drawn in the same heat as world champion and home favourite David Greene, Fredericks went out hard but, by the third hurdle, he was clearly lame, dropping back to complete the lap in eighth position.

To the pleasure of the home crowd, Greene nailed his flag to the pole in 48.98 seconds, posting one of the fastest qualifiers of the morning.

"I felt my hamstring pop over the first hurdle and by the second, I just couldn't accelerate," said Fredericks.

"I was determined to finish. I wasn't going to stop in the Olympics, but knew I couldn't go faster."

For Van Zyl it, was the continuation of a bad season.

"Three weeks ago Hennie [Kotze, his coach] wanted to pull me out, but I fought hard to be here," Van Zyl said.

Since April, Van Zyl had struggled to find the form which had taken him to the World Championships in 2005 and the Beijing Olympics in 2008, where he finished fifth.

Although he was in contention for the first half of the Olympic heat, the Tukkies athlete faded back to sixth in 50.31 seconds, missing the cut for one of sixth fastest finishers by 11 places.

Angelo Taylor won Van Zyl's heat in 49.29, while Puerto Rica's Javier Culson posted the day's fastest time of 48.33.

South Africa's hopes for the day, in the athletics, now rest with World and Olympic silver medallist, Khotso Mokoena, who competes in Friday evening's long jump qualifier.