The 35-year-old played an integral role as the Blades held firm to record a second consecutive clean sheet at Bramall Lane.
Ehiogu formed a near-impenetrable partnership with Matt Kilgallon and Blackwell believes the pair's muscular presence played a pivotal role in United's bright second-half display.
"The attitude of my players is first class and they wanted to try and win the game," he said.
"The two centre-halves for both teams were outstanding.
"Ugo looked back to his very best and we're talking about a lad who has played at the very highest level - that's how well he played.
"Kilgallon alongside him was immaculate as well. So much so that Cardiff couldn't get out of their half because the two of them were on top of Jay Bothroyd and Paul Parry. It allowed us to have a real high tempo in the second half."
James Beattie made his long-awaited return from injury with 10 minutes remaining and his presence caused havoc in the Cardiff penalty area during the closing stages.
But Blackwell insists that last season's top goalscorer will have to fight hard to regain his shirt on a regular basis.
"He has worked his socks off the last six weeks and he looked quite sharp in training," he added.
"He can work even harder now over the next two weeks.
"He knows the lads have been in form. Whoever is playing well and has got the shirt then they will get to keep it.
"If I say things and don't stick to it then I lose all sorts of credibility in the dressing room."
Cardiff boss Dave Jones was full of praise for his depleted side as they put up a brave resistance to United's physical approach.
Darren Purse and Roger Johnson were in imperious form at the heart of the defence and repelled everything that the Blades threw at them.
Jones said: "It was a game for men because it was very physical.
"We had four big hitters out and I thought the lads that came in were outstanding.
"But they had to be because it's a very difficult place to come and they're on a bit of a high. I think we showed a lot of quality today and a lot of good movement.
"We had the battling things you need as well because it's not just all about playing football - you sometimes need that battling side.
"For the neutral it must have been a good game to watch. It was tough but we came through I with a lot of credit."