The midfielder lit up a dour Selhurst Park encounter between two struggling sides on Saturday with a sensational volley.
It eased Palace clear of the drop zone and left Micky Adams still looking for his first win as United manager after 10 matches in charge.
Palace have now not let in a goal at home in more than 12 hours and the Blades rarely looked like threatening that miserly record.
But in a game which both teams were desperate not to lose, it was going to take something special to break the deadlock and Ambrose was the man to provide it.
The midfielder has endured a stop-start season due to injury but crashed in his fifth goal of the campaign in style from 20 yards.
The opening stages suggested the visitors would make a decent fist of it, with Neill Collins heading a good chance wide and Palace full-back Nathaniel Clyne blocking Richard Cresswell's effort on the goal-line.
But that was about as good as it got for the Blades.
At the other end Palace broke away when Wilfried Zaha played in James Vaughan, only for the Everton loanee to blaze over.
South Africa World Cup star Kagisho Dikgacoi joined the Eagles on loan from Fulham this week and almost marked his debut in spectacular style with a 25-yard volley.
United keeper Steve Simonsen managed to palm the fierce shot away and Ambrose scuffed the follow-up wide.
Ambrose nearly made amends after 20 minutes when he hammered in a 25-yard free-kick which took a slight deflection and forced Simonsen into a fine diving save.
United's crosses were causing occasional panic in the Palace area with goalkeeper Julian Speroni uncharacteristically flapping at one and skipper Paddy McCarthy heading another inches wide of his own goal.
After the break Speroni came out bravely to deny Cresswell and Dean Moxey warmed Simonsen's hands with a low drive.
But the game was meandering towards a bore draw until the 69th minute when Neil Danns won a header 30 yards out.
The ball bounced to Ambrose who, in a flash, had controlled it with his left foot before smashing it past Simonsen with his right for a truly memorable goal.
The Blades almost pulled one back but sub Marcus Bent's header was blocked on the line by a sea of Palace defenders.
Ambrose could have had a second at the end but he sent a far easier chance than the one he scored high over the top.