The Blades dominated but had to rely on two late goals to snatch a share of the spoils.
James Beattie headed United in front with his eighth league goal of the season midway through the first half.
But a well-taken volley from Joe Ledley levelled matters before ex-Liverpool striker Robbie Fowler and Gavin Rae gave Cardiff a commanding 3-1 lead.
A dramatic late comeback from the hosts saw Chris Armstrong pull a goal back with five minutes remaining before Chris Morgan's injury-time header secured a point.
"I hope the nature of the result is a turning point, but the main turning point has got to be for us to keep clean sheets. We can't keep conceding the goals we are doing," admitted Robson
"The first 45 minutes is as good a mixture of attacking play we've had. We caused Cardiff all sorts of problems and played some great stuff.
"I couldn't believe we came in at half-time 2-1 down. It was a huge task and the players showed great character, even the fans realised it wasn't a disjointed performance.
"The players deserved what they got, there's no way they deserved to lose."
Cardiff boss Dave Jones admitted it was hard to fault his side for their overall performance, but revealed he was disappointed at the way they folded at the end of the clash.
"I've just berated my players for that final five minutes when really for 85 minutes we were outstanding, but we have to defend better," he said.
"I can't fault the players, sometimes as a manager it's hard to swallow after a five-minute spell like that.
"But really we should not have allowed them back into the game.
"We should not have to come here and score four goals to get a result."
Jones is confident his side can be in the promotion mix-up at the end of the season.
"We've not come away with three points, but there's a long, long way to go," he added.
"If we keep playing like we can and stop being sloppy, we can be up there with the rest of them in this division.
"It's a hard league to get out of but we're getting better. There are a lot of positives, I just can't find the key to lock our defence."
PA Sport