AFC's Alex Erediauwa did well to curl the ball in towards Malahi Linton, but the Redbridge keeper was on hand to collect the ball, in the sixth minute,
At the other end, Milo Grimes stood strong to deny a powerful effort from Redbridge's number 8, while Sam Bishop headed away a cross from the following play.
Sudbury responded, as Kane Munday sprinted forward and set-up Linton, but the ball was too powerful, allowing the visiting keeper to win the ball well. At the other end, Adam Dunnage made a good clearance, while Malahi Linton headed away the resulting corner.
The Motormen kept pressing, and came close through a free-kick. The Yellows replied with a nice effort from Linton which flew just over the bar, while Alfie Cerulli saw his volley go just wide.
The visitors took the lead in the 31st minute as Redbridge's number 7 ran around home keeper Curtis Child and slotted home, despite Adam Dunnage's best efforts of a goal-line clearance.
The Yellows equalised on impressive terms, as Malachi Linton struck the ball home from outside the ball, past the visiting goalkeeper.
Sudbury looked to take the lead on the stroke of half-time as Sam Bishop set up Alex Erediauwa but his effort was saved well.
Half-time: AFC Sudbury 1-1 Redbridge Reserves
Redbridge started the second half strong, and regained the lead only a minute into the half, with a solo effort being struck low past Child. 1-2
In the 55th minute, Redbridge made it 3-1 as a nice ball is crossed in towards no 11 who tucked the ball home from close range.
Alex Erediauwa completed 57 minutes as he was replaced by George Tatum.
But it soon became 4-1 to the visitors in red, as nice team play saw a resulting shot beat keeper Child.
Danny Laws made his final set of changes of the match, as Callum Vincent and Tom Gardiner replaced Alfie Cerulli and Adam Dunnage.
The home side continued to battle on, and went close in the 78th minute as substitute George Tatum was played forward and struck the post, although the effort was flagged offside.
In the 86th minute, an AFC free-kick taken by AFC's Munday is crossed in but headed away by Redbridge. The visitors then broke forward and produced a shot which Curtis Child calmly saved.
Adam Hanson also came close for the Yellows, from Munday's cross late on, but the visitors held on for the victory.
Full-time: AFC Sudbury 1-4 Redbridge Reserves
AFC Sudbury: Curtis Child, Sam Bishop, Adam Dunnage (Tom Gardiner, 11), Tom Prentice, Alex Erediauwa (George Tatum, 57'), Kane Munday, Isaac Skunich, Alfie Cerulli (Callum Vincent, 63'), Milo Grimes, Malaki Linton.
Unused subs: Marcel Walker, Kie Dyer.
Ref: Anthony Abbs