Kansas City found itself eight games back of division-leading Detroit back on July 21, but has won 15 of 18, including the last seven after a three-game sweep of San Francisco, to move just a half game back of the Tigers.
Should they win again on Monday and a Detroit loss in Pittsburgh, the Royals would be in first place by themselves this late in a season for the first time since August 29, 2003.
"I like the way we're playing," Kansas City manager Ned Yost said. "I've got a lot of confidence in those guys. I've had a lot of confidence in them even when they weren't producing like they're doing now because I knew it would come somewhere down the road."
Kansas City will rely on righty Yordano Ventura in the opener. The 23-year-old right-hander won his second straight start on Wednesday in Arizona, as he held the D-backs to a pair of runs and struck out eight in six innings to run his record to 9-8, while lowering his ERA to 3.47.
"I didn't have a feel for my breaking ball or my offspeed [pitches], but I kept trying to throw it to try to get in a rhythm with it," Ventura said. "It was just one of those days when I didn't really have a feel for it."
Oakland, meanwhile, will counter with a pretty impressive young hurler of its own in 24-year-old righty Sonny Gray, who is 12-5 with a 2.87 ERA, but has lost his last two starts. Gray was awful on Wednesday against Tampa Bay, as he was tagged for seven runs (6 earned) in just 4 1/3 innings.
It's only the second time in his young career that he has lost back-to-back games.
"When you put your team in a hole like that, it puts a lot more pressure on the offense and it's harder to climb out of," Gray said. "That's just tough to do, especially when the other team is scoring so many runs early in the game."
Oakland stretched its lead in the American League West to four over the weekend, but was denied a sweep in its series with the Minnesota Twins, as it dropped a 6-1 decision in Sunday's four-game finale.
Kansas City took two of three from the A's earlier this month.