Sheikh Mohammed's Godolphin has outbid Coolmore to secure a colt out of Australian-bred New Zealand Group One winner Bounding for $4.1 million ($A5.9 million) at the Keeneland September sale.

By Curlin, the colt was knocked down to Godolphin's agent Anthony Stroud after a spirited bidding duel.

By Lonhro out of Believe'n'succeed, Bounding won the 2014 Railway Stakes at Ellerslie and was bought by US-based Stonestreeet Farm for $1.9 million at the 2016 Magic Millions Broodmare sale.

Her pedigree has been enhanced by her half-brother Anthony Van Dyck's win in this year's Epsom Derby.

"He's a very athletic horse, a lovely well balanced horse from a good farm and we liked him very much," Stroud said.

"He just had wonderful movement and athleticism."

The price was the highest paid at the Kentucky sale since 2010.