A 4-1 defeat saw the U's go into the bottom three for the first time this season despite the U's going ahead through Johnnie Jackson.
His goal was against the run of play and no-one could despute the fact that it was a thoroughly deserved victory for the Welsh strugglers.
The home side had the best of the possession and chances of the first half but Jackson's goal stunned them two minutes from half time.
They reacted well though and scored four goals without reply in the second period.
With the U's only above the home side on goal difference, it was important to get a positive result against Dave Jones' men in South Wales.
Geraint Williams made two personnel changes in his starting eleven, bringing in experienced duo Kevin Watson and Teddy Sheringham.
Kem Izzet dropped out for the first time this season after picking up his fifth booking last weekend, giving him a one match suspension, and Platt made way for Sheringham in attack.
Cardiff City boss Jones made four changes to his starting line up after the 2-0 defeat here at Ninian Park against Charlton Athletic during the week.
The biggest change was Jimmy Floyd Hasselbank returning up front after coming on as a second half substitute in that reverse against the Addicks.
Ina scrappy opening, it was Cardiff who were asking the most questions but there weren't any efforts on either goal until the twentieth minute.
Hasselbank couldn't get a clean shot away and Thompson had a shot blocked for a corner. Johnson's header from the resultant corner was cleared off the line by Kevin Watson, perfectly placed on the post.
On twenty six minutes, it was Hasselbank in the thick of things again as another shot was blocked before Gerken saved from McPhail. Almost immediately, Gerken looked like he got a fingertip to a Hasselbank shot, with the ball then rebounding to safety off Gerken;s far post.
Gerken bettered that save a couple of minutes later as he parried a thumping Whittingham free-kick to safety after Matt Connolly was booked for a foul on Thompson.
Hasselbank shot wide and Whittingham hit the side netting as the Bluebirds continue to apply the pressure. Gerken saved again in the forty second minute and it looked like the U's would be more than happy to go in at half time on level terms.
That wasn't the case though, but it was the U's who went ahead, somewhat against the run of play.
Kevin McLeod received the ball on the left and while being rounded booed for his Swansea links, cut back onto his right foot. His cross was exquisite and caused uncertainty in the Cardiff defence, allowing Johnnie Jackson to swoop.
The former Tottenham midfielder took a touch and after steadying himself, rifled a right foot shot high into the roof of the net.
Cardiff boss Dave Jones must have been stunned but Geraint Williams would have been happy with his players' resilience and then the break away goal.
Cardiff still had one more chance but George Elokobi blocked Hasselbank's effort just before the ref blew for half time.
If losing that goal late in the first half hurt Cardiff, their second half performance showed their character as they were straight on the front foot.
It only took them six minutes to level things up as Thompson scored with a near post header. Parry beat Elokobi and found Hasselbank, whose cross was powered home by his fellow striker.
Only five minutes later, the U's had a great chance to go back in front but as it happened, went behind.
Kevin McLeod latched onto a defensive mistake but his weak shot was saved before Cardiff went down the other end and scored through Whittingham.
A right wing cross found the Cardiff winger and his shot deflected off Karl Duguid on its way past Gerken.
It got worse for the U's ten minutes later as the best move of the match saw Hasselbank get a deserved goal. Whittingham set it up but the move started further back with some slick football and Hasselbank finished with a lovely near post finish.
Two minutes later, on sixty eight, Adam Virgo put through his own net to compound things and the U's were on their way to their worst defeat of the season. Even after the fourth goal, Cardiff looked more like scoring despite taking their foot off the pedal and results elsewhere saw the U's go into the bottom three.
U's: Gerken, Duguid, Virgo, Connolly, Elokobi, Yeates, Watson, Jackson, McLeod, Lisbie, Sheringham.
Subs: Cousins, Granville, Baldwin, Guttridge, Platt.
