The Englishman's second European Tour title came after a drama-packed final hole saw the trio go into a three-way play-off.
Defending champion Davies and England's Horsey, who had a hole in one at the second, exchanged blows throughout the final day.
With one to play, Horsey was one ahead of Davies and two clear of South Africa's Van Zyl, but took five from the middle of the fairway and six in total.
His double bogey left Davies a four-foot putt for the win, but the Welshman - one of the tour's finest putters - ran the effort two feet past the hole.
That allowed South African Van Zyl into a play-off with his par for what would be a maiden European Tour title.
However, Horsey, who headed into the final round as joint leader along with Davies, emerged strongest on the second hole of the play-off to follow up his victory at last year's BMW Open and move into the top 80 of the official world rankings.
