It's amazing ... Petra Ecclestone blew $85 million on Candy Spelling's 57,000 mansion, and she could still afford a wedding that rivaled the one recently thrown for those 2 kids in England.

Petra tied the knot with businessman James Stunt in Italy yesterday, in the same village where Tom and Katie got hitched.  But this wedding was a lot more expensive -- reportedly more than $5 mil -- and a lot grander.

For starters, Andrea Bocelli was there performing "Time to Say Goodbye," the first dance was courtesy of Eric Clapton, and the crowd then danced to The Black Eyed Peas.  BTW, Peas don't come cheap -- $2.4 million for the live appearance.

Petra -- the daughter of Formula One billionaire Bernie Ecclestone -- was decked out in a $130,000 Vera Wang special.

Guests guzzled wine at $6,500 a bottle -- Chateau Petrus, of course.

And, of course, Paris, Nicky and Kathy Hilton were there.

Wait till Petra Petra's dad gets the credit card statement.