Minnesota star running back Adrian Peterson rushed for 140 yards and two touchdowns as the Vikings edged the Steelers 34-27 at Wembley Stadium in London yesterday.  Matt Cassel started in place of the injured Christian Ponder and threw for 248 yards and two touchdowns, both to Greg Jennings.  Jennings ended with three grabs for 92 yards, while Jerome Simpson had seven catches for 124 yards for the Vikings, who improved to 1-and-3.  The Steelers had a chance to tie it late, but Ben Roethlisberger fumbled at the Minnesota 11 yard line in the final seconds after he was sacked.  Roethlisberger finished 36-of-51 for 383 yards with a TD and an interception for the Steelers, who are 0-and-4 for the first time since 1968.  Le’Veon Bell rushed for 57 yards and two scores and Jerricho Cotchery had five grabs for 103 yards and a TD in defeat.  The Vikings have a bye week coming up.