It is the first time Butler and Heigl have starred together
Romantic comedy The Ugly Truth, starring Gerard Butler and Katherine Heigl, has gone straight to the top of the UK and Ireland box office.
The film took £1.9m, fighting off competition from the Sienna Miller-starring GI Joe: The Rise Of The Cobra, which entered at number two with £1.7m.
Last week's number one, Harry Potter And The Half-Blood Prince, fell to third place.
The only other new release in the top 10 was The Orphan at number eight.
The horror movie, which has taken £570,146, is about a couple whose adopted nine-year-old girl appears to be responsible for a number of gruesome accidents.
UK TOP BOX OFFICE TOP FIVE
1. The Ugly Truth - £1.9m
2. GI Joe: The Rise Of The Cobra - £1.7m
3. Harry Potter And The Half Blood Prince - £1.3m
4. G-Force - £1.2m
5. The Proposal - £755,242
Source: Screen International
Disney's G-Force, which mixes live action and computer-generated animation, was this week's number four.
The film is about a trio of animated secret agent guinea pigs, voiced by Penelope Cruz, Sam Rockwell and 30 Rock star Tracy Morgan.
Sandra Bullock's The Proposal fell one place to number five, followed by action thriller The Taking Of Pelham 123 at six, and animation Ice Age: Dawn Of The Dinosaurs at seven.
In ninth place was comedy caper The Hangover, while biopic Coco Before Chanel, which stars Audrey Tautou as the eponymous fashion designer, rounded out the top 10.