George Sykes put Aveley down in the first half, but on the stroke of half Bobby Price’s audacious effort from the halfway line somehow found the back of the net after a poor goalkeeper.
An own goal saw Horsham equalize shortly after the restart, but Harry Gibbs restored the Millers’ lead.
Substitutes Daniel Ajakaiye equalized with two minutes remaining and an incredible turnaround was delivered in the fourth minute of stoppage time when Doug Tuck scored his first Hornets goal.
Di Paola said: “It was one of those games where I felt like we weren’t going to get anything anymore. There was bad defending but we came in with a winner which was great. .
“I was quite happy with the performance in general and I thought we were the better team. It was another game where I felt we could have been a little tough. We just couldn’t get that goal for us. put forward.”
Victory over Aveley took Horsham through to the first round of the FA Trophy for the first time since 2018. The Hornets will visit league rivals Folkestone Invicta in the next round on Saturday October 29.
Di Paola added: “We haven’t really done much in there so it’s good to get a win. It’s a cup in which, historically, the club has done very well, so we’re happy that we were able to progress to the next round.
“We have a tough draw in the next round. Folkestone are a good team but I’m happy we got the win.
New midfielder Oliver Knight, signed from Met Police last week, received his first start at Horsham and Di Paola was encouraged by the former Forest Green Rovers academy player’s debut.
He said: “He hasn’t really had a lot of time to figure out what we want him to do, but I thought it was a good time to dump him. He did well.”
Horsham returns to Isthmian Premier Matters this Saturday when he hosts Kingstonian.