Irish Olympian Aoife Clark held her nerve under intense pressure to win the Fidelity Blenheim Palace International Horse Trials in Oxfordshire.
Clark posted a clear showjumping round after closest challengers Jean Teulere and Clark Montgomery left no room for manoeuvre.
Frenchman Teulere and American Montgomery both finished on their cross-country scores of 45.5 penalties, which meant Clark could not afford a mistake aboard nine-year-old chestnut mare Fenyas Elegance.
And Clark did not disappoint, remaining on 44.0 penalties to take the £8,000 winner's purse and a title that numbers Zara Phillips, Mary King, Pippa Funnell and current world number one Andrew Nicholson among its former holders.
Teulere, eventing world champion 11 years ago, secured the runners-up spot on Matelot Du Grand Val because he finished closer to the cross-country optimum time of 10 minutes 10 seconds than Montgomery, riding Loughan Glen.
Sussex-based Gemma Tattersall was the highest British finisher in fourth spot on Arctic Soul, which again underlined her promise as a potential contender for the Rio 2016 Olympics
Clark, who rode Master Crusoe to seventh place at London 2012, conquered Blenheim just two hours after the Irish eventing team were crowned European junior champions in France.
"I knew I had to go clear," Clark said. "We've only had one showjumping rail down all year, but there was still pressure.
"To win here means a huge amount. This mare is just at the right stage to be looking at the (2014) World Equestrian Games and then Rio."
Clark was second with Fenyas Elegance at Chatsworth International in Derbyshire earlier this year, and then eighth in the British Open, and she added: "The horse was such a star this week.
"We knew she was in great form and peaking, but I couldn't have asked for any more from her. I will go home now and crack open some bubbly!"