Sebastian Janikowski, who signed a four-year, $14 million contract during the off-season, gave the Raiders a 10-9 lead with 1:54 remaining by kicking a 28-yard field goal.
Fourth-string Dallas quarterback Matt Nichols then tried to drive the Cowboys into field goal range and it appeared he might have done it when he threw a pass to a wide open Manuel Johnson near midfield.
Johnson would have had room to run his way into field goal range, but the ball slipped through his fingers and into the hands of Boyd, who went the distance untouched.
It was the pre-season opener for the Raiders. Dallas (1-1) opened its pre-season with a victory in the Hall of Fame Game over Cincinnati, but the Cowboys have yet to produce an offensive touchdown.
David Buehler kicked three field goals to give the Cowboys a 9-0 lead heading into the fourth quarter before Oakland scored on a 4-yard pass from backup quarterback Kyle Boller to Nick Miller with 5:05 to go.
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