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.
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.
5. Jack Strange
Strange was the best player in a first half that Barnsley dominated. He was commanding and poised on the ball and in the second brought the ball up calmly into midfield. The Hornets centre half won everything in the air and the Tykes attack looked toothless against him the second half. Photo: Charlie Crowhurst
6. Harvey Sparks
Harvey Sparks Photo: (Photo by Ben Roberts Photo/Getty Images)
7. Lucas Rodrgues
Lucas Rodrigues was good in midfield, he almost pulled one back for the Hornets just after the second half break where he broke free but his effort was a weak one. Photo: John Lines
8. Danny Barker
Barker played well in the middle of the park, combatting the strength of the Barnsley midfield, his link up play between the back four as well was also very good. He was replaced by Tom Kavanagh at the break. Photo: John Lines