Crystal Palace will take a narrow lead into the second leg of the Carling Cup semi-final after Anthony Gardner's header earned victory over Cardiff.
The visitors started the brighter but Joe Ralls could not beat Julian Speroni, while Ben Turner headed over.
Palace regrouped and went ahead on 43 minutes when Gardner scored from Darren Ambrose's cross from the left.
Kenny Miller had the ball in the net early in the second half but the goal was disallowed for a foul on Speroni.
Cardiff's Scottish striker also went close in the first period when his shot curled just wide.
Although Malky Mackay's side did not carve out too many clear-cut chances, they will be confident they have a good chance of overturning the deficit in a fortnight's time.
The Bluebirds hold the second best home record in the Championship and this was only their third loss in 15 games.
But the victory for Palace was a case of triumph over adversity given the virus that had hit Dougie Freedman's squad this week and they will hold the slight advantage as the two teams aim to become the first Championship side to reach the final since 2001.
Buoyed by having beaten Manchester United at Old Trafford in the last round, this performance will give the Eagles further heart, even if they found themselves under early pressure from a succession of long throw-ins by Aron Gunnarsson.
Turner failed to direct his header on target from one of them, while Palace keeper Speroni had to be decisive with his handling when saving Ralls' early shot. Miller also hit a curling shot from the right just wide.
Palace were being overrun in midfield but they began to redress the balance, retaining the ball better, while Wilfried Zaha showed some neat touches.
The highly-rated Zaha helped set up a good chance for Kagisho Dikgacoi, but the South African's shot was saved by Tom Heaton following Chris Martin's lay-off.
Heaton, the only Cardiff player who had featured in their FA Cup defeat by West Brom on Saturday, had looked comfortable dealing with several fizzing Darren Ambrose set-pieces.
But he was slow to reach another from the left flank and Gardner nodded in a simple finish from close range after the keeper was beaten in the air by Mile Jedinak.
Apart from that FA Cup reverse, Mackay's side have been on a good run of form. They responded strongly after the break and had the ball in the net when Miller headed in from a corner.
Referee Mike Dean had spotted a push on Speroni by Joe Mason, however.
As the second half wore on, there was a sense that Cardiff were content to settle for the 1-0 scoreline - they certainly did not lay siege to the Palace goal.
When they did manage to threaten, they were met with some resolute Palace defending, with former Spurs defender Gardner suffering a cut head as his side ensured a clean sheet.
The Eagles had a late scare when Peter Whittingham's deflected shot bounced narrowly wide, but they held on to the lead as they aim to reach their first League Cup final with the tie delicately poised.