With early game tensions at their highest, St. Louis shortstop Pete Kozma committed an error in each of the first two innings and starting pitcher Adam Wainwright made a classic fielding blunder that was ruled a base hit.
Only two of the five runs scored by the Red Sox during the first two innings were unearned, but if Kozma had not committed the errors and Wainwright had not let a popup fall in front of him the Cardinals would likely have escaped those two frames unscathed.
Even when a brilliant defensive play was made by a St. Louis player, it cost the Cardinals. Right fielder Carlos Beltran, making his first World Series appearance after playing in 2,064 regular-season contests, took a grand slam homer away from David Ortiz in the second inning only to suffer a rib injury when he slammed into the wall.
Beltran left the game and was taken to a local hospital for x-rays.
Ortiz, meanwhile, hit a two-run homer deep into the right field seats in the seventh inning off reliever Kevin Siegrist to pad the Boston lead and Jon Lester threw 7 2/3 shutout innings to get the win.
The Cardinals will attempt to even the series on Thursday when they send Michael Wacha to the mound to face John Lackey.
Ortiz then hit a grounder to second baseman Matt Carpenter and although the ball was a slow roller there was time to turn an inning-ending double play.
Carpenter's throw to Kozma, however, glanced off Kozma's glove and that miscue allowed Boston to load the bases.
Second base umpire Dana DeMuth at first ruled Pedroia was out at second base, but after a conference of all six arbiters that decision was overturned.
Napoli followed with a drive into the left-centerfield alley that brought home all three runners.
Boston's second inning began with Stephen Drew hitting a pop fly in front of the pitcher's mound. Wainwright called off his teammates and appeared ready to make the catch, but he stepped back at the last moment and the ball fell in front of him.
Pedroia followed with an RBI single and Ortiz next launched a fly ball to deep right that turned into a sacrifice fly when Beltran made his dazzling above-the-wall catch.
In addition to their fielding lapses, the Cardinals were unable to come through at the plate. St. Louis loaded the bases with one out in the fourth, but 2011 World Series MVP David Freese grounded into a double play. The Cardinals also stranded two runners in the fifth.