The Deans, who had scored 30 goals in winning their opening five games, were held 1-1 at Five Heads Park.
Horndean are six points clear of second-placed Moneyfields, while US remain unbeaten after five games, drawing three of them.
9. Horndean defend. Horndean v US Portsmouth U18s, Hampshire Combination League Picture: Chris Moorhouse (111020-22)
Horndean (red) v US Portsmouth in the Under-18s Hampshire Combination East Division. Picture: Chris Moorhouse Photo: Chris Moorhouse
10. McKenzie Morgan, nearest camera, and Jack Heath. Horndean v US Portsmouth U18s, Hampshire Combination League Picture: Chris Moorhouse (111020-21)
Horndean's McKenzie Morgan, nearest camera, and Jack Heath. Picture: Chris Moorhouse (111020-21) Photo: Chris Moorhouse
11. McKenzie Morgan, second left, and US Portsmouth player wearing 18 and not given on team sheet. Horndean v US Portsmouth U18s, Hampshire Combination League Picture: Chris Moorhouse (111020-20)
McKenzie Morgan, second left, battles for possession against US Portsmouth. Picture: Chris Moorhouse Photo: Chris Moorhouse