The Bluebirds, who lost the top of the table clash with QPR last weekend, salvaged a point to provide a boost to their promotion aspirations but have now won just one of their past six games and have fierce rivals Swansea breathing down their necks.
Keogh has a habit of rescuing City late on, with the on-loan Wolves man's only other goal this term a similar late effort to see off Millwall.
Cardiff started brightly enough but saw the wind taken out of their sails somewhat by the eighth-minute loss of Jay Bothroyd to injury, with Preston seemingly able to weather the hosts' second-half storm.
But to North End's well-deserved credit, particularly in the first half, it was difficult to tell at times which side were fighting relegation and which competing for promotion.
A drilled low free-kick from on-loan Stoke midfielder Michael Tonge looked to have proved the difference between the two teams midway through the opening 45 minutes, but the pressure remains firmly both on Preston boss Darren Ferguson and counterpart Dave Jones.
On a wintery afternoon, an early shot from Bothroyd proved to be the final contribution from the England international who was replaced with what appeared to be a hamstring strain.
Replacement Keogh almost proved his immediate worth, doing well to lay off the ball for Craig Bellamy to fire narrowly wide as the hosts started to turn the screw.
More good attacking play from City left most of the 21,151 present wondering when and not if the opener was going to come.
But the Lilywhites survived the early pressure and fought their way back into contention, before taking a shock lead through Tonge in the 26th minute.
Mark Hudson brought down Darel Russell on the edge of the penalty area and Tonge stepped up to drill a low free-kick past the helpless David Marshall, who was starting his first game since late September after Tom Heaton sustained a training ground injury in midweek.
Matters quickly went from bad to worse for Cardiff manager Jones who then lost centre-back Darcy Blake to injury.
The hosts had certainly gone off the boil and the remainder of the first half was an evenly-matched affair, with the scoreline only really threatened by two half-chances for Bellamy.
Cardiff started the second half with the same attacking mentality as they did the first, full-back Kevin McNaughton forcing a fine stop from Andy Lonergan who was matching everything thrown at him.
Michael Chopra was introduced in a bid to provide spark in attack but, with the hosts piling on the pressure, they were struggling to break down a resilient Preston rearguard.
Solid defending and a splash of good fortune was certainly the order of the day for the visitors in the second half, with Bellamy - at the centre of most things for Cardiff - unable to find a breakthrough.
Billy Jones cleared off the line from Gabor Gyepes in injury time but, with Preston seemingly heading for victory, it was left for Keogh to rewrite the story.