Pennie won World Championship silver in 2006
Great Britain's Fiona Pennie was left rueing a disastrous opening run as she failed to qualify for the semi-finals of the women's K1 kayak slalom.
Pennie missed a gate on her opening run, incurring a penalty of 50 seconds, as well as getting another two-second penalty for touching a gate.
And although her second run was quicker, Pennie came 17th - with only the top 15 progressing from the heats.
"After training for four years, it's pretty heart-breaking," she said.
"It's been a great experience, but I wish I could have experienced more in the semi-final.
"The 50-second penalty was a killer. It was a unanimous decision by all three judges.
"On the first run all our coaches thought it was in, and in our video it looked it, but I guess that's the way sport goes."
Pennie clocked runs of 160.06 and 99.00 seconds at the Shunyi slalom course in Beijing for a total of 259.06.
She was 72.87 seconds behind Elena Kaliska of Slovakia, who topped the heat standings in a time of 186.19 after two faultless runs.
China's Li Jingjing was second with Stepanka Hilgertova of the Czech Republic third.
The K1 semi-final takes place on Thursday.