The French-bred gelding outpaced 96 rivals in this marathon speed contest to defeat Adelfos, the mount of Switzerland's Markus Fuchs, by 0.06sec.
Gerry Mullins finished third for Ireland after an acrobatic feat that drew much clapping and cheering from the riders' stand.
Mullins had been pitched forward when Lismore landed steeply over the last fence and he was underneath the horse, with his arms wrapped around its neck as they crossed the finish.
John Whitaker had a far less adventurous ride on Everest Milton, who produced the slow clear round which was all that his rider asked of him. Milton will jump in one small class here before contesting Sunday's Grand Prix.
''That will be the test for him,' Whitaker said of Sunday's class. If the great horse is back to his best, he is a likely contender for the World Equestrian Games, which begin next month.Reuse content