Britain's Scott Brash claimed victory in the Horse Guards Parade in London in round 11 of the Global Champions Tour.
The defending champion and world number one won after a jump-off, edging out four-time Olympic gold medallist Ludger Beerbaum of Germany.
Brash, 28, is chasing Sweden's Rolf-Goran Bengtsson, who heads the GCT leaderboard with three events left.
Brash said: "It is a massive bonus to win. My horse was fantastic and that made my life easy."
Maikel van der Vleuten from the Netherlands came third, while 20-year-old American Katherine Dinan was fourth.
First prize was worth £120,000 for Brash, who is a certainty to be in Britain's squad for next month's World Equestrian Games in Normandy.