Starting pitcher Will Smith (4-4) pitched seven solid innings, giving up just five hits and two runs and striking out five for the win.
Kansas City took the lead in the first inning when Billy Butler grounded into a fielder's choice to score Alcides Escobar. Oakland tied it in the second with an RBI-single from Brandon Moss and took the lead in the fourth off a Josh Donaldson solo home run.
Athletics starter Brandon McCarthy (6-4) pitched 6 2/3 innings, gave up seven hits and three runs and struck out four in the loss.
The third and final game of the series is set for Thursday at 7:10 p.m. CT at Kauffman Stadium.
For updates, stay tuned to SB Nation Kansas City. For more on the Royals, make sure to check out the discussion and analysis over at Royals Review. For the Oakland perspective, head to Athletics Nation. For more news and notes from around the world of professional baseball, visit Baseball Nation.