Spacey plays a maths professor who leads his students astray
Las Vegas gambling drama 21, which stars Kevin Spacey, has entered the UK and Ireland box office at number one.
The film, based on the true story of a group of US students who employ card-counting techniques to cheat a casino, made £1.6m in its opening week.
Schoolboy drama Son of Rambow held firm at number two, while last week's number one, 27 Dresses, fell to number three.
But George Clooney's American football drama Leatherheads only managed to touch down at number six.
The movie, which had a star-studded premiere in London's Leicester Square last week, took just £475,000 during its opening weekend.
UK AND IRELAND BOX OFFICE
1. 21 (£1,649,845, including £142,016 from previews)
2. Son Of Rambow (£749,760)
3. 27 Dresses (668,659)
4. The Spiderwick Chronicles (£676,798)
5. Step Up 2 the Streets (£662,180)
Source: Screen International
Fantasy film The Spiderwick Chronicles and urban dance movie Step Up 2 the Streets both fared better, sitting at numbers three and four respectively, despite having been in cinemas for a month.
Down one place at seven was Dr Seuss adaptation Horton Hears a Who, the animated tale of an elephant trying to save a microscopic world on a speck of dust.
The week's biggest faller was Never Back Down, which has drawn comparisons to Karate Kid, which dropped from four to eight.
Martin Scorsese's movie about the Rolling Stones, Shine A Light, debuted at nine with takings of £338,000, including previews.
And the top 10 was rounded off with murder mystery Pathology.