The latest sequel also had a worldwide total of $680.1 million.
No other solo superhero - not even Batman or Spider-Man - has managed this kind of business.
"Iron Man 3" had the second-biggest domestic debut ever, behind the $207.4 million start over the same weekend last year for "The Avengers," which teamed Downey's Stark with other Marvel Comics heroes. The new sequel surpassed the $169.2 million opening for 2011's "Harry Potter" finale, the previous second-place debut.
In a distant second place was "Pain & Gain" with $7.6 million, followed in third place by by "42" with $6.2 million.
The top 10 films of the weekend were:
1. "Iron Man 3," $175.3 million ($175.9 million international).
2. "Pain & Gain," $7.6 million.
3. "42," $6.2 million.
4. "Oblivion," $5.8 million ($6.5 million international).
5. "The Croods," $4.2 million ($17.4 million international).
6. "The Big Wedding," $3.9 million ($2.5 million international).
7. "Mud," $2.2 million.
8. "Oz the Great and Powerful," $1.8 million.
9. "Scary Movie 5," $1.4 million ($4 million international).
10. "The Place Beyond the Pines," $1.3 million.
The Associated Press contributed to this report.
