The Blues’ under-18s got the better of the young Latics thanks to goals from Lewis Lambert, Seb Mason and Jack Porter.
The victory at the Sheepmount sent Mark Birch’s side into the northern final of the youth knockout competition.
And United’s progress was seldom in doubt as they had much the better of proceedings in Tuesday’s semi-final against opponents who had a man sent off late on.
Lambert struck early on and then Mason doubled the advantage after the break with Porter wrapping things up late on.
The game at the Sheepmount saw Carlisle prevail (Image: News & Star)
The game was watched by United’s first-team head coach Mark Hughes and his senior coaching staff including Frankie McAvoy, Gavin Skelton and Jack Cudworth.
They saw the Blues’ up-and-coming teenage players take control of the tie in the opening stages.
After Jonah Lowes had an early attempt blocked following an impressive cross-field move, Carlisle went in front on eight minutes when Mason’s cross was headed home by frontman Lambert.
United went on to have the better of the first half even though Oldham threatened with an Alfie Hughes cross that just dipped over the Carlisle bar, and Will Decandia’s off-target header after he was picked out by Hughes’ free-kick.
Carlisle, though, also came close to more first half goals, first when the pacy Amaru Smith beat Oldham keeper Harvey Hampson to a long ball but just found the angle too tight to finish.
Lowes sent a free-kick over the bar for the Cumbrians and then fired just wide with another shot from the edge of the box – before Will Hatton’s cross was volleyed against the bar by Lambert.
After the break, United pushed for a second, with Mason denied by recovering defenders after the Blues won the ball back in Oldham territory.
Soon afterwards, Mason did make it 2-0, finishing from close range after Hatton had beaten his man on the Carlisle right in the 62nd minute.
Seb Mason was among United's scorers against Oldham (Image: Richard Parkes)
Lambert and Smith were denied further goals in the Oldham box before Hayden Atkinson, at the other end, made an important last-ditch challenge to prevent Solomon Butterfield getting in for the visitors.
Mason and Tai Bell were denied by good Hampson saves before Porter added a third in the 88th minute, the defender slotting home after Carlisle had worked a short corner on the right.
The game then ended in bad-tempered fashion as Carlisle players reacted angrily to Oldham defender Isaac Adelaja’s challenge on Mason which left the United forward in need of treatment for a facial injury.
Adelaja was shown a straight red card while United captain Atkinson was booked for his part in the melee of players that followed the incident.
Carlisle’s progress in the competition will send them through to a regional final against Blackpool – and the chance to turn the tables on the side who beat the Blues in this season’s FA Youth Cup.
The young Seasiders defeated Mansfield Town 4-2 in their semi-final last week.
United: Worth (Grainger 88), Hatton (McDonough 78), Hodgson, Atkinson, Porter, Rigby, Rafferty (Tonge 70), Lowes, Lambert (Bell 78), Mason, Smith (Stewart 16).
Goals: Lambert 8, Mason 62, Porter 88.
Oldham: Hampson, Hughes, Adelaja, Steele, Amos, Mulcahy (Potts 75), MacBride (Howard 63), Johnson, Decandia (Koch 46), Butler, Butterfield.