Horndean dumped AFC Totton out of the Hampshire Senior Cup at the Testwood Community Stadium.
The Deans claimed a 4-1 triumph over their Southern League division one south hosts.
Mark Smith netted twice, while Harry Jackson and Jack Maloney were also on target for Michael Birmingham’s Wessex League premier division outfit.
Totton lost goalkeeper Shane Murphy to injury during the early skirmishes of the tie.
And Horndean compounded the Stags’ misery when they took the lead on 22 minutes.
Jack Lee fed Jackson, who beat a defender before firing home.
Jackson, Lee and Smith all went close to a second but Totton prevented further damage before the interval.
The home side managed to level soon after the break.
But that only served to inspire the Deans, who hit the front again courtesy of Smith.
Benny Reed had an effort saved before – at the other end – Kieran McGee had to be alert to prevent a second equaliser.
Maloney settled any nerves when he made it 3-1 and with the Deans piling on the pressure, Smith completed the job.
Elsewhere, Gosport Borough led twice before being dumped out on penalties by Bournemouth Poppies.
A late leveller from the home side saw the scores level at 2-2 after 90 minutes and sent the tie to spot-kicks.
And a first-half goal earned Fareham Town a place in the next round following a 1-0 win over Petersfield Town at Love Lane.