Royals 3, Athletics 0: Jason Vargas scattered three hits in a complete-game gem and Omar Infante belted a two-run homer as host Kansas City posted its second win of the four-game series versus Oakland.Nori Aoki joined Infante with two hits and a run scored for the Royals, who have won 17 of their last 21 and remained a half-game ahead of Detroit in the American League Central. Salvador Perez added a sacrifice fly in the win. Josh Donaldson ripped a two-out double in the first inning to extend his hitting streak to 10 games. Oakland mustered just two more singles and saw its lead in the American League West dip to 2 1/2 games over the second-place Los Angeles Angels. After struggling in two starts since undergoing an appendectomy, Vargas (9-5) recorded his first win since July 2 and notched his 11th complete game and sixth shutout of his career. The 31-year-old, who retired the final 23 batters he faced, did not walk a batter and struck out four in the dominating performance.Aoki had a one-out single in the second before Infante deposited a 2-0 fastball from Scott Kazmir (13-5) over the wall in left field for his sixth homer - and first since June 27.GAME NOTEBOOK: Kazmir fell to 4-7 in his career versus Kansas City after permitting three runs on seven hits in seven innings. ... Vargas' complete game was the Royals' third in seven contests. ... Kansas City OF Alex Gordon went 0-for-3 with two strikeouts to see his six-game hitting streak come to an end.