Neil Warnock labelled Cardiff's 1-0 victory at Leicester as their best win of the season.
Victor Camarasa's brilliant stoppage-time goal earned the visitors their first away win this term.
Neil Etheridge also inspired the visitors as he saved James Maddison's penalty and made a host of other fine stops.
He denied Jamie Vardy, Demarai Gray and Ricardo Pereira, with Cardiff now four points above the Premier League drop zone.
"It's the best day since we've been back in the Premier League," Warnock said. "It's the best performance of the season, by an absolute mile. Defensively I thought we were outstanding.
"There are a few teams down there who didn't expect to be. That's difficult mentally. We've always known we would be down there.
"I thought we deserved to win. We limited them. If we'd have been precise in the final third we could have scored three or four.
"I'm really proud how they put their bodies on the line. We've come along way, we've improved so much since the start of the season.
"We've bust a few coupons haven't we, with the way Leicester have been playing."
Camarasa's 25-yard effort in the second minute of stoppage time sealed Cardiff's first away win in the Premier League since April 2014 and Warnock reserved praise for Etheridge.
He said: "The penalty was iffy, he (Sean Morrison) has blown him (Maddison) down but you get them given against you. Some give it, some don't.
"It's about time he made up for Man United's third goal. He is improving all the time."
Leicester's regular penalty taker Vardy was taken off six minutes before Maddison's miss.
The substitution, for Kelechi Iheanacho, was jeered by the home fans and Maddison missed his second straight spot-kick after seeing one saved in the Carabao Cup shoot-out against Manchester City.
Leicester failed to build on their surprise Christmas victories over Chelsea and Manchester City.
Boss Claude Puel said: "We will see with Maddy (how the miss affects him), it's a big disappointment for him. He has a lot of responsibility and has learned a lot.
"We're frustrated. We knew before it would be tough but we played a team with another style of play after Chelsea and City.
"We tried to push until the end to find a clinical edge. We were unlucky but it's football. The period when we dominated we needed to score.
"When you play against a team like Cardiff we need to win the game 1-0. A draw was a minimum and it's difficult to accept."
Puel also justified his decision to take off Vardy in the 68th minute.
He added: "I manage my team on what I see. He was tired and it's normal. They were tired, Marc (Albrighton) like Jamie. We tried to find a solution. To push with fresh players giving their best."
