Ambrose kept his nerve to score from the spot with two minutes remaining after Derby midfielder Paul Green had fouled Neil Danns.
The Rams looked set to end Palace's run of 11 home games without defeat when Jamie Ward's stunning strike put them in front for a second time, but Palace were not to be denied.
Stephen Pearson had put Nigel Clough's side ahead early on with his first goal of the season, but Palace were deservedly level at the break when Dean Moxey scored his first goal for the club following his move from Derby in January.
The point moves the Eagles four points clear of third-bottom Sheffield United, while Derby are still not out of the woods but they are nine points better off than the Blades.
Palace came close to taking the lead six minutes in, when on-loan Rams goalkeeper Frank Fielding denied James Vaughan and Steffen Iversen failed to convert the rebound.
And less than a minute later the visitors were in front when Pearson kept his composure to slot home with his left foot from 12 yards out.
Palace responded and Fielding was once again in the thick of the action as he palmed away Ambrose strike from just outside the penalty area.
And it was no surprise when the Eagles levelled after 20 minutes, with Moxey giving Fielding no chance with a rasping left-foot drive from 25 yards out.
The home side were dominant and Ambrose tried his luck from long range but Fielding tipped the ball around the post.
Moxey clearly fancied his chances of doubling his tally and he let fly from long range once again but this time Fielding made the save early in the second half.
But the Rams were back in front after 62 minutes when on-loan strike Ward drilled a stunning right-foot strike from long range which flew past Julian Speroni and into the top-right corner of the net to stun the Selhurst Park faithful.
Palace boss Dougie Freedman threw caution to the wind by bringing on strike duo Pablo Counago and Wilfred Zaha in a bid to salvage something from the game.
Central defender Anthony Gardner spurned a chance to equalise with 19 minutes remaining when he rose to meet Ambrose's free-kick but failed to hit the target with his header.
But Palace salvaged a point two minutes from time when Green fouled Danns and, after referee Jon Moss pointed to the spot, Ambrose slotted home from 12 yards.