Barnsley took the lead after just three minutes when a cross sailed over Lewis Carey’s head for Nicky Cadden to tap home.
The Tykes doubled the advantage on ten minutes when the Hornets again failed to deal with a cross and McAtee was there to slot home at the back post.
McAtee made it 3-0 after 26 minutes after Jordan Williams delivered a delightful ball into McAtee who saw Carey off his line and produced a delightful chip.
But Horsham were simply excellent in the second half and were unfortunate not to get a goal their attacking play so richly deserved.
But who stood out for Horsham? Here are Sam Pole's ratings from the game.
13. Reece Myles-Meekums
Reece Myles-Meekums was good when he was brought on, his runs down the right were excellent providing some much needed energy. Photo: John Lines
14. Tom Richards
After coming on Richards was a thorn in the side of the Barnsley defence, his runs and quick feet proved a great asset to the side. Photo: John Lines
15. Doug Tuck
Tuck came on to provide stability in the midfield in the late stages and he performed well in the midfleld after coming on as a sub Photo: John Lines
16. Tom Kavanagh
Kavanagh was the engine in midfield after coming on his energy in midfield was crucial in Horsham's fightback performance in the second half. Photo: Charlie Crowhurst