Both Welsh regions took two points from the draw in a game that was dominated by the boots of out-halves Dan Biggar and Dan Parks.
Biggar provided 18 points with five penalties and a drop goal, with a further drop goal scored by Ospreys centre James Hook.
Parks kicked all of his side's 21 points - five penalties and two drop goals - as the Blues overcame an early 9-0 deficit and finished strongly.
The first half saw the sides cancel each other out for the most part. The highlight was the attacking impetus of Blues number 8 Xavier Rush, who made one memorable 40-metre break and then also put full-back Dan Fish clear with a neat pass out of the back door.
The Ospreys had the best of the set piece battle, especially in the scrum which was responsible for two of Biggar's first three penalty shots.
Biggar's first kick was a monster penalty which just crept over from five metres inside his own half.
From 9-0 down after 21 minutes, the Blues started to get a bigger percentage of possession which saw Parks put over a drop goal and four minutes later he struck a penalty.
But with both sides making mistakes, they had to rely on their respective number 10s to get the scoreboard ticking.
After Blues lock Bradley Davies was sent to the sin-bin by French referee Christophe Berdos, Biggar restored the Ospreys' six-point lead with his fourth penalty of the evening.
In the final minutes of the opening half, Parks and Biggar swapped a penalty and drop goal respectively as the Ospreys went in at the interval armed with a 15-9 advantage.
The drop goal fest continued right at the start of the second half with Hook putting over three more points. But that was cancelled out with a fourth Parks penalty as the stop-start nature of the contest continued.
Referee Berdos ran out of patience with the serial infringing and he sent former All Black Jerry Collins to the sin-bin for failing to release a player on the deck.
Despite being a player down, the Ospreys were next to score as Biggar converted his fifth penalty after the Blues had been caught offside.
But Cardiff hit back as the pinpoint Parks was successful with his fifth penalty kick, reducing the home lead to 21-18 with 59 minutes on the clock.
And the scores were level at 21-21 after Parks put over his second drop goal, 13 minutes from time.
The Ospreys twice tried to regain the lead but both Biggar and Hook missed the target with drop goal attempts late on, and the Blues battled their way to a well-merited two points.
The result leaves Cardiff just four points behind fourth-placed Leinster, with a game in hand. The Ospreys, meanwhile, have moved up to third ahead of their trip to the Newport Gwent Dragons in two weeks' time.
Giving his assessment of the drawn derby, Ospreys captain Alun Wyn Jones said: "We're pleased to get something out of it, and at the same time we're disappointed we didn't get the win.
"Out there, it felt as though we were a score away from breaking them, but it was a typical derby game. Yes, we're disappointed but I suppose as a neutral you'd probably say that it was a fair reflection of the game.
"It was about solid defences I suppose, on the whole, but there were a few decisions from us that we'll probably rue when we look over the game in the week.
"I think we'll be disappointed when we've picked and gone when we had numbers a few times," he admitted.
|Ospreys Score Card|
|Cardiff Blues Score Card|