Meet the Spartans scored a slight upset at the Cineplex over the weekend, edging out the blood-soaked epic Rambo for first place at the box office. The critic-proof parody tallied $18.7 million in its first three days of release, while Sylvester Stallone's latest comeback vehicle trailed close behind at $18.1 million, according to boxofficemojo.com. Katherine Heigl's rom-com 27 Dresses placed third with a $13.6 million take, followed by monster movie Cloverfield at $12.7 million -- a precipitous 68% percent drop for J.J. Abrams' much-hyped flick. Rounding out the top five was Diane Lane's thriller Untraceable, which took in a respectable $11.2 million.