Romford beat Harpenden Town 3-1 in their FA Cup extra preliminary round replay at Mayesbrook Park on Wednesday.
Boro had been held to a 1-1 draw in the first meeting at the weekend, when Steve Carvell's free-kick was cancelled out by Mulik Rickman.
But they took the lead after only eight minutes of the second encounter thanks to L'heureux Menga.
The visitors were back on terms on 15 minutes, though, as Josh Rodrigues netted and it remained all square until the first minute of the second half, when Christian Adu Gyamfi restored Romford's lead.
Menga and Carvell had been booked just before the break and Abdulmojeed Shogbeni and Aundre Wholas-Spencer had their names taken on 53 minutes.
Jesse Olukolu became the fifth Boro player to be shown a yellow card just before the hour mark, but sealed victory in the third minute of injury time when sending Harps keeper Eman Olajide the wrong way from the penalty spot.
As well as pocketing £1,125 in prize money, the win earned Romford a trip to Kensington & Ealing Borough on August 21.
Romford start the new Isthmian League North Division season with a home game against Maldon on Saturday (3pm).
Romford: Simeon, Kauzeni, Wholas-Spencer, Hayes, Nelson, Shogbeni, Toussaint, Menga (Campbell 64), Adu Gyamfi, Carvell (Barnett 82). Unused subs: Haysman, George, Ekoja, Bullman.
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