Callum Robinson gave Cardiff a lead but a last minute equaliser from Gassan Ahadme sent the visitors home happy.
Cardiff City (First 60 minutes): Allsop, Ng, McGuinness, Simpson, Bagan, Wintle, Ralls ©, R. Colwill, Ojo, Evans, Etete.
Cardiff City (Final 30 minutes): Alnwick, Romeo, Benjamin, King, T. Davies, Adams, Rinomhota, Tanner, Robinson, J. Colwill, Watters.
Cambridge United (First half): Stevens, L. Bennett, R. Bennett, Beckett, Dunk, Digby, Hoddle, Brophy, Lankester, Barton, Okenabirhie.
Cambridge United (Second half): Mannion, Scales, Okedina, Morrison, Andrew, Thomas, Simper, Janneh McConnell, Yearn, Ahadme.