The series recognises success in the world’s six four-star horse trials.
William was in pole position after his two CCI**** victories, at Pau (with Oslo) in 2011 and Kentucky (Parklane Hawk) in April this year. But the competition went to the wire, with William beating Andrew by just one point.
It is the closest finish since the series’ inception in 2008.
“That was close!” said William afterwards. “I knew Andrew was on fantastic form and to win by one point was nerve-wracking.”
William admitted that he wondered if missing Luhm ¼hlen was a mistake.
“It was too close for comfort, but I’m lucky to have had such a good horse as [last year's Burghley winner] Parklane Hawk. The HSBC FEI Classics is a great series and much appreciated by riders,” he added.
William and Parklane Hawk had two fences down but hung onto third place – just 0.1pen ahead of Oliver Townend and Andrew’s former ride, Armada, in fourth.
If he had hit another fence, Andrew – who was third in the Classics last year – would have become the first non-British rider to win.
It is the third time that William has won the Classics. He took the title in 2008 and 2010, while Oliver Townend won in 2009 and Mary King became the first woman to win it last year.