Cray Valley forced a replay after a 1-1 draw against Charlton Athletic, who are five divisions above the Millers.
Charlton captain Scott Fraser opened the scoring, and an own goal from Lucas Ness levelled the game.
A second-round tie against Gillingham awaits the two teams, who will face off again at the Artic Stadium.
Fraser opened the scoring in the ninth minute after he took the ball around Sam Freeman and scored in the empty net.
The Millers’ best chance of the half came in the 21st minute when Kyrell Lisbie was found on the edge of the box, but his shot was blocked.
In the 34th minute, Freeman performed a stunning save to prevent Charlton from doubling their lead when Slobodan Tedic’s shot was flying towards the top corner.
Cray Valley equalised in the 48th minute and sent the 1,998 Valley fans wild after a low-drilled cross from Lisbie was knocked in by Ness.
The Addicks responded with a barrage of attacks, Charlie Kirk had two big chances, including a chance at the back post where he blasted his shot high over the bar in the 50th minute, followed by a one-on-one saved by Freeman in the 53rd minute.
The Millers almost took the lead in the 72nd minute when a Denzel Gayle cross found Sonny Black, who failed to direct his volley towards goal.
In the 84th minute, Julien Anau almost grabbed the winner for Cray Valley as he found himself in a lot of space outside the box, but his shot sailed wide.
Cray Valley had another opportunity, this time an Adam Coombes free kick, which was struck well but at the keeper in the 90+1st minute.
Wave after wave of attacks were launched against the Millers, but they proved a rock-solid defence and held out for the draw.

Charlton Athletic: Walker, Thomas, Ness, Fraser, Abankwah (Asiimwe 59), Kirk (May 59), McGrandles (Watson L 72), Edun (Watson T 59), Campbell (Lea burn 72), Tedic, Anderson, Subs Not Used: Maynard-Brewer, Dobson, Hector, Blackett-Taylor,
Cautions: None

Millers: Freeman, Williams, Lee, Tumkaya, Black, Parker (Coombes 68), Ademiluyi, Vigor (Anau 68), Lisbie (Gayle 59), Ibrahiym, Asiedu. Suba Not Used: Chambers, Ovenden, Ekpetita, Gilchrist, Tuner, Wickes
Cautions: None

Match Officials
Referee: Benjamin Speedie
Assistants: Ryan Whitaker and Gareth Viccars
Fourth Official: Tom Reeves