For two thirds of the game YM held their own, only to be overrun midway through the second half.
Arthur Grout gave Borough the lead before they had Tayt Trusty sent off for a second yellow.
But Laith Fairnie promptly headed home and then repeated the feat for a 3-0 advantage, Zack Tarrant making it four and Lachlan Byrd sealing YM’s fate with a fifth with ten minutes left.
YM ran and ran right to the end.
In the semi final Eastbourne will play Brighton U21s at Lancing – while Worthing face Three Bridges in the other semi.
See pictures from Eastbourne Borough 5 Horsham YM 0 on this page and those linked and get the local football action in the County Times on Thursday and the Eastbourne Herald on Friday.
1. Eastbourne Borough v Horsham YM pictures by Lydia and Nick Redman (23).jpg
Eastbourne Borough v Horsham YM, Sussex Transport Senior Cup Photo: Lydia Redman : Lydia and Nick Redman
2. Eastbourne Borough v Horsham YM pictures by Lydia and Nick Redman (21).jpg
Eastbourne Borough v Horsham YM, Sussex Transport Senior Cup Photo: Lydia Redman : Lydia and Nick Redman
3. Eastbourne Borough v Horsham YM pictures by Lydia and Nick Redman (47).jpg
Eastbourne Borough v Horsham YM, Sussex Transport Senior Cup Photo: Lydia Redman : Lydia and Nick Redman
4. Eastbourne Borough v Horsham YM pictures by Lydia and Nick Redman (31).jpg
Eastbourne Borough v Horsham YM, Sussex Transport Senior Cup Photo: Lydia Redman : Lydia and Nick Redman