Gary Ablett was forced to reshuffle his defence after failing to reach agreement with Leeds United to play Paul Huntington.
Johnny Mullins moved inside to partner Michael Raynes with James Vincent coming in at right back.
Youth team leading scorer, Tom Fisher, won a place on the bench.
Peter Thompson's second goal in a week set County on the way to a record-equalling Cup victory.
The Northern Ireland international pounced in the 13th minute to score from the rebound after Dave King had parried Paul Turnbull's shot.
And nerves were eased further seven minutes later when Michael Raynes and Michael Rose combined to play David Poole clear and the winger hit his shot across King into the bottom corner.
The rampant Hatters extended their lead when Dean Hamlin brought Thompson down in the box and Car Baker made no mistake from the spot for his eleventh goal of the season.
And it could have got even better for County in the final moments of the first half. First Liam Bridcutt brought a brilliant save out of King who tipped the dipping 25-yarder over the bar. Then, following Rose's corner, Baker clipped the bar from the edge of the box.
The Terrors had their moments, though, and could even have taken the lead on 11 minutes when Simon Parker beat two defenders before shooting narrowly wide.
Tooting started the second half brightly but couldn't find a way through the strong County defence and the game entered a quiet period.
But, midway through the half, the Hatters produced the move of the match involving several players that ended with Paul Turnbull scoring his first of the season.
And, within a minute, he should have scored again when he missed a real sitter at the far post with the goal at his mercy.
The man-of-the-match atoned for that miss after 72 minutes, though, when he made it 5-0 following brilliant approach work from Baker.
The visitors, to their credit, kept trying to play football and they were unlucky not to grab a consolation five minutes from time when Craig Pitterson's volley looked to be goalbound until it hit Raynes and bounced behind for a corner.
A minute later County should have made it six when Johnson angled a pass behind the Terrors defence. The two subs, Greg Tansey and Tom Fisher, seemed to get in each others way though and the move ended when Fisher snatched at his shot and pulled it wide.



















