Zack Willett opened the scoring with his 35th league and cup goal of the campaign.
Midfielder Tommy Tierney wrapped up the win by scoring twice, with all the goals coming in the first half.
Horndean still have two games in hand on Portchester and travel to the On-Site Group Stadium next month.
Pictures by Keith Woodland
Horndean still have two games in hand on Portchester and travel to the On-Site Group Stadium next month.
![Horndean's Rudi Blankson, right. Picture: Keith Woodland](https://www.portsmouth.co.uk/webimg/b25lY21zOjllYzlhNGFmLTcyZmEtNDY2NC05YWQ1LTk1N2RlNzRjNmQ5MTplMzdjZGJhZS1mNjM0LTRlODItOTRjZS1jZjMyNDlkMzRmOTc=.jpg?crop=3:2&trim=&width=640)
17. Horndean's Rudi Blankson, right.
Horndean's Rudi Blankson, right. Picture: Keith WoodlandPhoto: Keith Woodland
![Tommy Tierney about to score his second goal and Horndean's third. Picture: Keith Woodland](https://www.portsmouth.co.uk/webimg/b25lY21zOjQ1YzRkMzllLWU5ZDQtNDVjNC1iN2I1LTE5ODJmOWQ5NTM4MjowMmFiZTZjMi0yMzJlLTQ1ZTMtODk0ZC1iZGNlYzMyZTQ1MzE=.jpg?crop=3:2&trim=&width=640)
18. Tommy Tierney about to score his second goal and Horndean's third.
Tommy Tierney about to score his second goal and Horndean's third. Picture: Keith WoodlandPhoto: Keith Woodland
![US Portsmouth (maroon/blue) v Horndean. Picture: Keith Woodland](https://www.portsmouth.co.uk/webimg/b25lY21zOjM1MmYxNmU0LTUyMDQtNDJkNi04MGIwLTUzZWU3ODg5M2EwYTpiNDJkODc5ZS1jYTczLTRmMDctYTFmOC01YzQ0NDRhZjQzMTQ=.jpg?crop=3:2&trim=&width=640)
19. US Portsmouth (maroon/blue) v Horndean
US Portsmouth (maroon/blue) v Horndean. Picture: Keith WoodlandPhoto: Keith Woodland
![Horndean captain Sam Hookey (white). Picture: Keith Woodland](https://www.portsmouth.co.uk/webimg/b25lY21zOmNlZGQ0MGEwLWE1MzEtNDI2ZC05NjY2LTI5YTAyMzEwNzQ2ZDozMTIxOTFkNS0xMTRmLTQ4NWEtYTNjOC02M2UzMmVkNTlmMmY=.jpg?crop=3:2&trim=&width=640)
20. Horndean captain Sam Hookey (white)
Horndean captain Sam Hookey (white). Picture: Keith WoodlandPhoto: Keith Woodland