For 70 minutes, the Rebels weren't at the races as Maidenhead showed more will to win the contest and had opened up a three goal cushion.
But after being strictly second best, the introduction of Kieran Gallagher, back from suspension, changed the complexion of the semi final and in a rousing finale, Slough came close to forcing extra time.
They pulled back two goals, had another one ruled out, struck the bar and also saw a relieved Magpies defence clear following an almighty goalmouth scramble.
"You couldn't fault the players in the last 20 minutes but you have to ask yourselves, why they weren't up for it in the first 70 minutes" said a disappointed Browne.
"If you can't be motivated for a Cup semi final, then you have to start questioning some players commitment. But having said that, we battled well in the last quarter."
"And why the referee ruled out the goal I don't know. He originally signalled a goal but then said that the free kick was indirect even though he didn't give a signal to say that it was."
That came after Keith McPherson had already stooped to head home Rebels first goal. Mark Hawthorne had been impeded on the left and after a lengthy delay, Gallagher's free kick flew over everyone and into the top corner. The Rebels supporters behind the goal turned from cheers to boos as referee Steve Phipps awarded a goal kick much to everyone's surprise, including the Magpies players.
The important question though was why the game had started after coming through a 4pm inspection. Incessant rain throughout turned the pitch into a quagmire, particularly in the centre of the pitch.
Maidenhead's direct approach, bypassing midfield with long balls for their pacy forwards saw them rain shots in on Steve Mautone, back in goal after his hand injury.
After Steve Daly had blocked Ricky Ibe's goalbound shot on the line, the Magpies went in front on 22 minutes when Lee Channeli fired home at the far post after Chris Ferdinand's corner had been headed on by Ibe.
The only serious test for home keeper Richard Barnard saw him leap acrobatically to his right to somehow keep out Michael Gilkes's 30 yard free kick which was headed in the top corner.
With the slope in their favour in the second period, Rebels hopes must have been high of turning the game around.
But on 54 minutes an error from Mautone gifted the ball to Ibe on the edge of the box and he gleefully shot into the unguarded goal to double the lead.
Steve Stott, victim of a vicious over the top tackle from Jamie Jarvis in the first period, won the ball to release Hawthorne whose fiercely struck 35 yard effort cannoned off the bar with Barnard rooted to the spot.
But a difficult task for the Rebels became almost impossible shortly after when after a bout of head tennis in the Slough box following a Ferdinand free kick, first half villain Jarvis headed home the third.
But with 20 minutes left, Gilkes cross was partially cleared to Anthony Howard, his low cross shot was diverted home by McPherson's head to give Slough hope.
Going forward with renewed vigour, Gilkes was just off target with another free kick. Steve Daly planted a header straight at Barnard before Gallagher had his free kick ruled out with seven minutes left.
As the game entered injury time, Sammy Winston was brought down by Tom Hickey and Simon Ullathorne confidently despatched the spot kick.
The Rebels pressed in the remaining minutes and despite causing several scares, they couldn't force the equaliser and it was a relieved Magpies side who greeted the final whistle.
For the second successive year, the Rebels have bowed out of the county cup at York Road, they will be hoping not to make it a hat-trick next season as this term has petered out to nothing.
Slough Town Line Up
- 1 Steve Mautone
- 2 Antony Howard
- 3 Steve Daly
- 4 Steve Stott
- 5 Keith McPherson
- 6 Simon Ullathorne
- 7 Sammy Winston
- 8 Mark Hawthorne
- 9 Neville Roach 15
- 10 Michael Bartley
- 11 Michael Gilkes 12
Maidenhead United Line up
Barnard, Ferdinand, Morley, Kelly, Jarvis, Jeffrey, Hickey, Ibe, Channell (Connor 83), Rake (Scott 83), Ulasi. Subs (not used): Rose, Saunders, Hart.