South African Olympic medal hopeful Shaun Rubenstein fell tantalisingly short of reaching the Olympic men's 1000 metre K1 final in a thrilling semi-final at the Shunyi Olympic Rowing-Canoeing Park, but said that the race would only serve to motivate him for his crucial 500m semi-final on Thursday.

The East Rand speedster was first out of the starting shoes and dictated the pace of the semi-final from the outset. He kicked shortly after the 500 metre mark, and went into a clear lead that had the other seven potential finalists in the nine-boat semi-final scrambling to stay with him.

The gamble to charge to the front from halfway only just failed to produce a stunning result, as the trio of Australian Ken Wallace, Kiwi ace Ben Fouhy and Swede Marcus Oscarsson overhauled him in the final 100 metres to the finish, leaving him fourth and out of the final.

"I went to the front and stayed there, but to keep these guys at bay is not easy," said Rubenstein. "With 150 metres to go I thought I had it, and then a bit of a monkey jumped on my back. If you lose concentration and miss one stroke these guys get half a boat length on you and at this level it is impossible to make that up."

"I was good enough to win for 900 metres, not a thousand. That was my problem," he said, adding that the stacked semi-final had been very competitive.

"I had two world champions, one Olympic champion, a junior world champion and another Olympic silver medallist in my heat, with three to go through to the final. Having said that I rate myself as one of them, and I came her to win, which makes it disappointing," he added.

"But the positive is that I have shown that I have the speed for the 500m semis, and that is very encouraging," he added. "I know I have the speed. I know I have the guts. All I have to do is put it all together. I am disappointed now but hopefully that will fuel me (for my 500m semi final)."

Mokoto fell short of making the C1 men's final, but posted a time that was a full six seconds faster than his time in his heat, showing the rapidly improving stature of the 19 year old Wattville talent. That personal best time was despite a bad start.

""I got splashed by the starting shoe dropping and I missed two strokes at the start, but after that I got into a really good rhythm," said Mokoto. "The water got a bit choppy in the last fifty metres as well, when I was trying to kick. But I am happy with my performance, and proud for my country."

On Thursday Rubenstein races his 500m K1 semi-final, along with Calvin Mokoto's 500m C1 semi-final and the women's K2 semi-final featuring Michele Eray and Bridgitte Hartley.