It was all about where United would finish in the top seven as they made the Coronation weekend visit to Sutton for their final scheduled league away game of the season.
And they earned a fifth spot finish and a visit to Valley Parade for the first leg next Saaturday courtesy of a second half fight back and a late Joe Kizzi own-goal.
Jack Robinson was in for the suspended Jon Mellish, with Alfie McCalmont for Ryan Edmondson the only other change.
Jack Armer filled in on the left side of three centre backs with Robinson on the left and Barclay on the right as mobile wing backs.
McCalmont volleyed high as the Bkues looked for a bright start, and Angol went close with a firm header as the yellow shirts responded.
And it was the hosts who took the lead on 16 minutes when Boldewijn nicked the ball to Kouassi. It opened up for the strike and Holy could do nothing as it nestled in his bottom corner.
United showed in fits and starts and Dennis rattled the bar with a fierce free kick after Moxon had rolled it his way as the remainder of the first period ticked along relatively quietly.
The Cumbrians upped the pace after the break with Patrick lively on both flanks. Moxon put one straight at Rose as he tried his luck from distance and a drillec cross across the face of the area was agonisingly just in front of two onrushing attackers.
Blue shirts pushed forward and they got their deserved equaliser when a throw from Barclay caused issues. It eventually hit Beautyman before Kizzi lost his balance and sent it over the line.
Donovan out one wide from what was a rare late chance, and the point was enough to secure the play-off place and the double-header with the Bantams.
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Goals
Sutton United - Kouassi (16)
Carlisle United - Kizzi (84 og)
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Bookings
Carlisle United - Robinson (47)
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Teams
Sutton United - Rose, Kizzi, Hart, Goodliffe, Milsom, Ajiboye, Beautyman, Smith, Boldewijn, Kouassi, Angol (Wilson 76). Subs - Dickinson, Rowe, Gambin, Neufville, Dundas, Fadahunsi.
Carlisle United - Holy, Barclay, Huntington, Whelan, Armer, Robinson (Garner 66), Guy (Edmondson 78), Moxon, McCalmont, Patrick (Charters 78), Dennis (Gibson 66). Subs - Kelly, Senior, Harris.
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Match officials
Referee - Darren Drysdale
Assistant Referee 1 - Daniel Cook
Assistant Referee 2 - Nicholas Dunn
Fourth Official - Andy Bennett
Observer - Philip Knight
Coach - Andy D'Urso
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Attendance - 4,771 (1,366 Carlisle fans)