Underneath Barry Geraghty, the pre-race favourite made a slow start to the race and settled in third place as he negotiated the opening few fences.
However, having held first spot for the majority of the course, Jason Maguire struck the third from last fence on second favourite Overturn and Simonsig took advantage by hitting the front.
The collision ended Oveturn's challenge, leaving Simonsig with a clear passage for home. Baily Green made a late dash, but the seven-year-old leader held off the confrontation to cross the line uncontested.
Tom Scudamore's His Excellency, who went off as an 80-1 chance, took third place.