By Rosalba O'Brien

LONDON (Reuters) - Beijing Olympic champion Matthew Mitcham gave a thin smile of resignation as he realized he would not be in Saturday's final to defend his 10-metre platform diving title.

The Australian earned the highest single-dive score in Olympic history on his final dive in Beijing, propelling him to gold and making him the only non-Chinese to win a diving gold in the 2008 Olympics.

In Saturday's morning semi-final, however, the 24-year-old, who has battled injury and missed last year's world championships in Shanghai, struggled to keep up with a strong field at the London Games.

After he over-rotated on his last back two-and-a-half somersault, his exit from the competition, just outside the cut in 13th place, seemed inevitable.

British pin-up Tom Daley, who nearly failed to qualify for the semi-final after a lackluster performance in Friday's preliminaries, put in a much more solid set of dives on Saturday to qualify for the evening final in fourth.

Daley will face stiff competition for a medal from China's own teenage sensation, Qiu Bo, Qiu's compatriot Lin Yue, American David Boudia and the two in-form German competitors, Martin Wolfram and Sascha Klein.

(Editing by Clare Fallon)