Leaders EP were 8-0 ahead at half-time and they have now scored 26 goals in three league games, after scoring seven in their previous two matches.
Lee Garnham blasted home four goals, George Gaskin netted his second successive hat-trick, Joe Shelley and Barney Boutwood both scored braces and Charlie Oatway was also on target.
It was a bad night for former East Preston boss Trevor Waller, whose Midhurst side were 3-0 down after just 20 minutes.
Garnham got the opener with a header from a Gaskin cross, before Shelley struck after an individual run.
Gaskin then struck twice, from Oatway and Garnham passes respectively, before Oatway made it 5-0 from Gaskin’s cross.
Matt Axell set Gaskin up for his hat-trick and Garnham then netted his second from Oatway’s assist.
Shelley headed home to make it 8-0 at half-time from Axell’s corner and EP kept going in the second half.
Substitute Boutwood lobbed home from 25 yards and Garnham then completed his treble to make it 10-0 after Boutwood’s shot was saved.
Garnham crossed for Boutwood’s second, before Garnham netted from Paul Brown’s cross to complete the scoring.
It is EP’s biggest win since November, 2009, when they also beat Midhurst – 8-0 – when Waller was East Preston’s manager.
It was EP manager Dominic Di Paola’s biggest win as a County League boss and he said: “It was pretty comprehensive as they had a bad night and we had a really good one.
“We had nine chances in the first half and scored eight, so were pretty clinical, and they looked pretty disheartened after 20 minutes when we’d already scored three.
“We talked at half-time about keep going and still taking our chances as it was a good opportunity to boost our goal difference, which we did.”
On whether he felt sorry for Midhurst, Di Paola said: “I like Trevor, their manager, but we had to do what was right for us. It was a good opportunity to win comfortably and comprehensively and score some goals, so I didn’t really feel sorry for them at all.”
EP are at Kent League Corinthian in the FA Vase second qualifying round on Saturday and Di Paola said: “It’s a nice break from the league and all the players are excited about it.
“It’s a nice day out and we’ll go there to try to win.”
EAST PRESTON: Bryant; Duncan, S.Di Paola, O’Hagan, Hibberd; Shelley, Axell, Barnard, Oatway; Gaskin, Garnham. Subs: Boutwood, Gibbs (Gaskin, Shelley 50), Brown (Di Paola 70), Keet, Clark.