The young Bluebirds suffered a damaging defeat in their Professional Development League South fixture at Crewe.
Cardiff had Keenan Patten sent off for a second bookable offence during the away teams second defeat in four days following a 2-1 loss at Sheffield United.
City made four changes to their starting line-up against the Blades with goalkeeper Jordan Duffey, Connor Davies, Sam Reynolds and Sam Parsons called up.
They would have qualified for the PDL play-off semi-finals with a win at Crewe and could have gone top of the table, but they lost to a Crewe team who were bottom of PDL North.
This was only their seventh win of the season and ended a run of nine successive defeats in all competitions, a run which stretched to December.
Cardiff scored first when the prolific Dan Griffiths, going round goalkeeper Sam Booth before rolling the ball into goal.
Crewe’s equaliser was scored by Matthew Fenton four minutes later and the teams were level at 1-1 going into the second half.
Kieron Evans went close to giving Cardiff the lead with a sublime curling effort from the edge of the penalty after 63 minutes. The shot was too good for goalkeeper Booth but rebounded off a post.
Crewe went ahead for the first time when Connor Heath scored (73 mins) and City had Patten dismissed nine minutes later.
Malach Linton added Crewe’s third goal during injury time.
Under-18 Crewe Alexandra: Booth, Allen, Woodthorpe, Odipe, Fenton (capt), Southern, Djalo, Robbins, Linton, Heath, Onyeka. Subs: Hartshorn, Walklate, Lokko.
Under-18 Cardiff City: Jordan Duffey, Connor Davies (Owen Pritchard 54), Ryan Kavanagh, Ryan Reynolds (Siyabonga Ligendza 48), Joel Bagan, Keenan Patten, Sam Parsons, Sam Bowen (capt), Harry Pinchard, Kieron Evans, Dan Griffiths. Subs: George Ratcliffe (gk), Rubin Colwill, Owen Pritchard, Smith.
Cardiff’s remaining Professional Development Under-18 League fixtures:
Tuesday 9 Bolton Wanderers (away, 11am)
Saturday 13 v Burnley (home at Cardiff International Sports Campus, Leckwith, 11am)