On Saturday, the story got even better as both the Royals and Indians won, while the rest of the division - Detroit, Minnesota and Chicago - all took losses. The co-leaders improved to 10-4 as Kansas City blanked Seattle, 7-0, and the Indians pounded Baltimore for the second straight day, 8-3.
Cleveland was powered by second baseman Orlando Cabrera, who went 2-for-4 with four RBI and three runs. Cabrera got things started in the second inning, driving in the first Cleveland run on a fielder's choice and coming around to score on Matt LaPorta's double.
In the 3rd inning, Cabrera singled home another run and scored and capped off his performance with a two-run blast in the 7th.
The Indians amassed 13 hits overall and seek to sweep the three-game series on Sunday. Likewise, the Royals are looking for a sweep of the Mariners.
The Cubs haven't had much to cheer about this season, but the 8-3 win over the NL West leader got them back to .500, at 7-7, and into the thick of the NL Central race.
Castro has been solid all along, his 4-for-5 effort boosting his team-leading batting average to .397. Called up early in 2010, Castro made a bid for rookie of the year by batting .300 over 125 games.
The Cubs are just two games behind the Reds in the division with St. Louis and Milwaukee tied for second place 1 1/2 back. Chicago will try to take the series at Colorado with a win Sunday afternoon.