Jason Euall keeps Mark Kennedy at bay as the Saints take the spoils
A controversial penalty from David McGoldrick after 11 minutes earned struggling Southampton a vital win in their fight against relegation.
The result brought an end to Cardiff's 13-match unbeaten Championship run and hurt their play-off hopes.
Mark Kennedy was penalised for handling in his own goal area after good work from Jason Euell and McGoldrick struck.
The Saints climbed one place to third from bottom while Dave Jones' side dropped to sixth in the table.
Cardiff City boss Dave Jones: "I don't think we performed anywhere near what we are capable of. I think possibly four out-field players did their jobs and the rest didn't turn up today.
"It's hard to swallow... It's a harsh decision for the penalty when you're looking for a little bit of luck.
"I wished the linesman's eyes had been as sharp [in the second-half] as they were in the first-half because it's a clear-cut penalty when the [Southampton] lad hands it back to the keeper.
"... But full credit to Southampton - they worked harder than us and we didn't really cause the keeper any great concern."
Ivan Sproule's injury-time goal ensured Bristol City's unbeaten league run stretched to nine games while leaving Southampton deep in relegation trouble.
City's Bradley Orr saw an early penalty saved and Saints hit the post twice before Dele Adebola latched on to Gavin Williams' pass to put the Robins ahead.
Kayne McLaggon tested home keeper Adrian Basso after the break and Jason Euell missed a tap-in from six yards.
And Saints paid dearly when Sproule raced the length of the pitch to score.
Bristol City boss Gary Johnson:
"Southampton put us under pressure but we defended when we had to and earned our win.
"Things are going very well for us and we are confident about making the play-offs, not in an arrogant way, but because we have faith in one another."
Southampton manager Mark Wotte:
"I can't fault them for what they did in the second half. But we play to score goals and didn't, which is why we are in our current position.
"I think we have better quality strikers, but at the moment we are finding it hard to get goals and that has to change.
"I can't believe we lost. The least we should go home with is a point."
Venue: Vicarage Road Date: Saturday, 7 February Kick-off: 1500 GMT Coverage: Full-match commentary on BBC Radio Solent on 96.1fm & Hants DAB, & the odd score update on BBC Radio 5 Live & BBC Sport website
Saturday's Championship match between Watford and Southampton has been postponed following this week's adverse weather conditions.
According to a statement on the Watford website: "The risk to the general public if the game went ahead could have potentially been too high."
Crowds at St Mary's have dwindled since relegation from the top flight
Southampton boss Mark Wotte has put the Saints' lowest ever league attendance at St Mary's down to the weather.
Tuesday's last-gasp 2-1 home defeat by Sheffield United was watched by just 13,257 supporters.
The match only went ahead after a number of pitch inspections and safety considerations, following heavy snow.
Wotte told BBC Radio Solent: "We had 17,000 on Saturday, they all went home satisfied with the performance. Today, I think it's more about the weather."
He continued: "I thought it was silent in the stadium in the second half especially when you go all the way to try to win.
"I think there was a very late reaction in support of the players but I know we have to earn that support. I'm not blaming the crowd, I'm just working with the players to do a better job."
The result leaves the Saints facing a grim battle to avoid relegation with just 15 matches left.
This is a battle that we lost, but we haven't lost the war yet
Southampton head coach Mark Wotte
The new lowest league attendance beats the previous worst figure of 14,226 against Coventry City in October.
Two months before that game, just over 11,000 turned up to watch the Carling Cup victory over Birmingham City.
St Mary's opened its doors for the first time back in 2001 after the club switched from the intimacy of the Dell.
Sell-out crowds of 32,000 regularly followed Southampton in the Premier League at the new ground before relegation in 2005.
But that is a far cry from the plummeting attendances this season. Saints have won just once in front of their own supporters in the Championship in this campaign and face the prospect of relegation to the third tier of English football for the first time since 1960.
Last Saturday, around 500 Saints fans went on a protest march from Southampton city centre to the stadium to voice concerns over the way the club is being run.
Saints lie second bottom in the Championship and three points off safety. On Saturday they travel to fellow strugglers Watford.
And Dutchman Wotte is confident of Southampton surviving.
"This is a battle that we lost, but we haven't lost the war yet," he said.
Jamie Ward's late winner gave Sheffield United all three points at Southampton.
Ward's low strike in the dying seconds stunned the Saints just moments after Andrew Surman's fierce shot appeared to have given the hosts a deserved point.
The Blades had taken the lead in the first half through Greg Halford, who headed home Nick Montgomery's cross.
The Saints dominated after United's Darius Henderson saw red for a clash with Jan-Paul Saeijs but were unable to break through until the late drama.
The crowd of 13,257 was the lowest league attendance at St Mary's.
Southampton boss Mark Wotte:
"A point does nothing for us and we needed three points so I had to push people forward and we got caught out.
"We have not lost the war tonight, we have only lost a battle and we have to keep on fighting.
"Every game is massive for us from now on and we need to win them all."
Sheffield United boss Kevin Blackwell:
"Jamie took his goal superbly well and we were delighted to see the ball fly in off the post.
"There was a lot of competition to sign him (from Chesterfield) in January but we are pleased to have got him.
"My lads showed tremendous spirit and I thought we deserved it."
Saganowski has scored twice since returning from a loan spell
Southampton striker Marek Saganowski says he is fully committed to the club, after making an impact since returning to the Championship strugglers.
The Pole recently spent a loan spell with Danish side Aalborg as part of cost-cutting measures at St Mary's.
He told BBC Radio Solent: "When I was sent to Denmark I wasn't happy because I felt good at Saints.
"I've got a year and a half left on my contract here and I want to play for this club."
Saganowski netted the equaliser in Saints' 2-2 draw at Norwich on Tuesday - his second goal in three matches since returning from Denmark.
"It was a big disappointment to be left on the bench, because I thought I did well in the previous game. The goal was my answer to the staff for leaving me out," he said.
The 30-year-old scored 10 goals in 13 appearances when he first joined Saints in January 2007, on loan from French side Troyes.
Jordi Gomez is on a season long loan spell from Spanish side Espanyol
A Marek Saganowski double saved 10-man Southampton a point against play-off contenders Swansea City at St Mary's.
Ex-Saints trainee Garry Monk gifted his old team the lead as his poor back-pass was pounced on by Saganowski who scored in his third successive game.
The Swans equalised when Spaniard Jordi Gomez smashed home from 25 yards before Southampton were reduced to ten men after Lee Molyneux was dismissed.
Gorka Pintado's struck the Swans ahead before Saganowski's late leveller.
Southampton manager Paul Wotte said:
"I am pleased we fought our way back into the game against a team like Swansea, who are one of the best in the division at the moment.
"But we want to be about three points at St Mary's.
"We need home wins to get ourselves up the table and at the start of the game I expected us to get the victory but it was not to be.
"Marek Saganowski took his goals very well, the first he perhaps took too much time and I was shouting 'shoot' at him from the touchline but the second he was much quicker and it was a great finish."
Swansea City manager Roberto Martinez said: "The environment was quite difficult and we know we can play a lot better.
"Their two goals were very sloppy on our part but we have taken another two points towards our tally.
"The level of performance was good but not very, very good like we expect.
"But we have to be realistic, at the beginning of the season we would have been delighted to have come to St Mary's and be disappointed with a point - it shows how far we have come."
