Hornchurch crashed out of the FA Trophy against local rivals Aveley in an upset at Bridge Avenue on Saturday.
Urchins had already put out Berkhamstead, Basildon United, Oxford City and Dulwich Hamlet, while Millers had made their way past Bowers, Taunton Town, Biggleswade and Carshalton Athletic.
That had earned both £13,700, with another £5,250 on offer, as well as a place in the last 16, on a chilly January afternoon.
And the Isthmian League North Millers made sure their name would be in the hat at the expense of Premier outfit Hornchurch amid no shortage of drama.
And only eight minutes had been played when the Millers took the lead in controversial circumstances.
Alex Akrofi had already seen a header from James Goode's cross comfortably saved by Joe Wright, while George Skyes had scuffed a Jonathan Nzengo cross straight at the Urchins keeper.
But Akrofi then went down under a challenge from Nathan Cooper, who appeared to have won the ball, and Shad Ngandu converted from the spot - thankful no doubt to his mum who had delivered his boots to the ground after he had forgotten to bring them himself.
Urchins settled into their rhythm, despite the setback, and Rickie Hayles flicked a long throw from Matt Johnson beyond the far post on 20 minutes.
Remi Sutton had penalty claims ignored by referee Lloyd Wood, when looking to get on the end of a cross from the right, and the ball came off the far post, before the Hornchurch defender was spoken to.
The hosts had a let-off when Wright spilled a deflected free-kick and smothered the loose ball, while Ronnie Winn had a free-kick saved by David Hughes after Sam Mvemba fouled Mickey Parcell and was shown a yellow card.
Cooper had his name taken for a challenge on Akrofi, with Wright saving Jason Raad's free-kick from the edge of the box, and George Saunders then sliced wide from another Johnson long throw, before Chris Dickson had a shot deflected behind.
Aveley were incensed when Clark challenged Nzengo in front of their dug out, but no further action was taken by Wood.
But the referee pointed to the spot again in stoppage time when Saunders spread the ball out wide to Parcell, who did well to get to the byline and flashed in a cross that hit an Aveley arm.
Dickson stepped up to score from 12 yards and leave the tie back in the balance at the break.
And Dickson was close to putting Urchins ahead three minutes after the restart, flashing a volley from a long throw just over the crossbar.
The hosts were reduced to 10 men on 51 minutes, though, when Parcell went in on Raad, who was left rolling on the athletics track.
And Aveley took the lead a minute later when the resulting free-kick was cleared to Nzengo, who sent a superb ball into the box for Harry Gibbs to head home.
Wright grabbed a speculative 25-yard effort from Akrofi at the second attempt on the hour mark, while Urchins saw a Saunders free-kick deflect off a leg and be smothered gratefully by Hughes.
Dickson had a shot blocked from Marvin Morgan's right-wing cross on 71 minutes, but Akrofi then spun into the box and saw his effort rebound out to Wyan Reid, whose shot was deflected behind.
Hayles headed just over from Winn's corner with 12 minutes remaining, while Charlie Stimson saw a close-range effort saved by Hughes from a long free-kick into the box.
Stimson had a shot blocked, after Dickson, Sutton and Morgan combined in a quick break on the left, with Morgan putting a far post header wide.
But Aveley had penalty claims for handball waved away, when Sykes headed goalwards from a corner six minutes from time.
Urchins kept pushing, but Aveley held firm to record another giantkilling and keep their dreams of a trip to Wembley alive.
Hornchurch: Wright, Parcell, Sutton, Lee (Stimson 65), Hayles, Johnson, Saunders, Clark (Morgan 46), Dickson, R Winn (Christou 84), Cooper.
Unused subs: Dutton, Glenister, Hassan, G Winn.
Aveley: Hughes, Nzengo, Mvemba, Goode (Allen 80), Gibbs, Mochalski, Reid, Ngandu, Sykes, Raad, Akrofi.
Unused subs: Martin, Chawner, Hossack, Servietis, Bragg, Scammell.
Attendance: 589.
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