It was there for the taking for Fox who went into the final round with a one-shot lead, and stretched it to three after bouncing back from a second hole bogey with three straight birdies.
With Fox and Horsfield tied at the 16th tee, the Kiwi went bogey-birdie-bogey to card an even par 71 and finish two shots behind the Englishman.
Fox will now head jets to the US PGA Championship at Southern Hills in Oklahoma for his 12th major appearance. A consolation from today's result is that the second placing should secure him a spot in next month's US Open.
The top 10 players over four events on the DP World Tour, starting last week at the British Masters where Fox finished ninth, earn a spot in the field at The Country Club in Massachusetts. Another strong showing at the Dutch Open (May 26-29) or the Porsche European Open (June 2-5) should do enough for Fox to make his fourth US Open.
The Kiwi world number 106 could also jump back into the world top 100 tomorrow as he takes plenty of form into the US PGA Championship, the second major of the year and his first since last year's Open Championship.
It's been an impressive run of form for Fox since returning to Europe following a two-month break in New Zealand in the wake of his victory at the Ras al Khaimah Classic in February.
Today's result at the Rinkven International Golf Club in Antwerp was his third straight top 10 finish and places him sixth on the DP World Tour standings. Fox has already amassed €566,439 (NZ$943,160) in prizemoney in 2022 as he heads to the lucrative US PGA Championship where first place earns US$2,160,000.
But there will probably be a feeling on that flight across the Atlantic Ocean that he let one get away leading what wasn't the strongest chasing pack with a three-shot lead and 11 holes to play.
Starting with a one-shot lead, Fox lipped out a par putt at the second hole to move back to 10-under and a tie at the front with what was just his second three-putt of the week.
He then took the solo lead straight back with a 26-footer for birdie at the third and followed that up with a brilliant approach at the fourth to get within five feet and another birdie. Fox then nearly chipped in for eagle at the fifth and rolled in a third straight birdie to take a three-shot lead.
Horsfield made an impressive 33-foot birdie to cut the lead to two at the seventh hole before Fox picked up another shot with a nine-foot birdie putt at the eighth.
The lead was reduced to two at the turn when Fox found the trees on the par fourth ninth, and then stuck by a tent for his third shot and needed a drop. A brilliant chip gave Fox a chance to save par but he walked away with bogey.
Fox still had a two-shot lead on the 12th tee but a birdie for Horsfield on the par three and a bogey for Fox at the 13th saw the two players level with five to play.
The Kiwi gave up the lead for the first time since the third round on the 16th hole with his fourth bogey of the final round but rebounded with an eagle putt on the penultimate hole, getting to within two feet to take birdie. Horsfield however responded with a birdie putt to retain a one-shot lead heading to the last.
The Englishman found a sandy path with his tee shot on the last but hit a brilliant approach to the green while Fox mis-hit his second from the rough and found the greenside bunker, all but conceding the tournament.
