Sylvester Stallone's action movie, co-starring Jason Statham, Dolph Lundgren, Bruce Willis and Arnold Schwarzenegger, holds off competition from Angelina Jolie spy thriller Salt to land in first place in the UK.
Toy Story 3 slips to number three, bringing to an end its month-long reign at the top of the chart. Two new entries, horror remake Piranha 3D and family film Marmaduke, round out the top five.
Elsewhere, Inception drops to number six, while The Last Airbender and The Sorcerer's Apprentice are the biggest fallers. The summer blockbusters both plummet five spots to land at numbers eight and ten respectively.
The UK box office top ten in full:
1. (-) The Expendables - £3,910,596
2. (-) Salt - £2,166,715
3. (1) Toy Story 3 - £2,090,277
4. (-) Piranha 3D - £1,487,119
5. (-) Marmaduke - £1,243,789
6. (2) Inception - £1,063,679
7. (4) Knight And Day - £825,692
8. (3) The Last Airbender - £586.576
9. (6) Step Up 3D - £507,942
10. (5) The Sorcerer's Apprentice - £439,527