And the A's and Blue Jays are two of the clubs currently at the center of it all.
Red-hot Oakland, winners of a season-high six straight after a 7-2 win in Tuesday's series opener in Toronto, entered that one with sole possession of the second Wild-Card, just one game behind the AL West-rival Angels.
The Blue Jays sit further back -- four games behind the A's after their loss on Tuesday. But wins in the last two games of the series, beginning on Wednesday, would further tighten the race.
"When you consider what Oakland is doing and how well they have played, and you can point to a number of teams around baseball, there is a lot more competitive nature to the way the schedule has unfolded," Blue Jays manager John Farrell said. "And I think once we get deeper into August, and everyone gets back into their division almost exclusively ... if one team gets hot, it can create some separation.
"But on the other hand, you would think there might be a battling back and forth that might keep things tight until to the end. This has been much tighter than what I think many anticipated."
Rookie A.J. Griffin will take the mound for Oakland in the middle game at Rogers Centre, while Ricky Romero gets the call for Toronto.
The right-handed Griffin hasn't been in the big leagues for long, having made five starts, but he's been solid so far, and against some big-name opponents, too. In his last start, Griffin held the Yankees to two runs in six innings, with his fastball-curveball combination working particularly well.
"That's all pitching is, is adding and subtracting velocity and going after guys," Griffin said after his last start. "We play a kid's game, we're just trying to have fun out there. And we're having more fun right now, winning games, having a good time."
A's: Power surge continues
Oakland entered Tuesday tied for the Major League lead in home runs since the All-Star break with 18, and rookie catcher Derek Norris, who was 1-for-30 in his last nine games coming in, clubbed his third long ball of the season in the second inning to put the Blue Jays in an early hole.
Shortstop Cliff Pennington, sidelined since July 20 with left elbow tendinitis, did not make the trip to Toronto, and if his elbow doesn't improve in the next few days, he'll make another trip to see a doctor.
With Pennington on the 15-day disabled list, Brandon Hicks and recent callup Eric Sogard have split time at shortstop, with Hicks playing against left-handers and Sogard against right-handers.
Blue Jays: Romero looking to rebound
Left-hander Ricky Romero will oppose Griffin on Wednesday night, and he'll be looking to snap a five-start losing skid. Romero has an 8.33 ERA during that span.
In his last start, the Yankees hit Romero particularly hard, as he gave up 12 hits and six runs in six innings on July 18.
Farrell said on Tuesday that injured slugger Jose Bautista could start swinging a bat by the end of this week. Bautista has been on the 15-day disabled list since July 17 with left wrist inflammation.
Oakland Left-hander Travis Blackley posted a career-high eight strikeouts in his start for the A's on Tuesday. On Friday, Tommy Milone fanned a career-high 10 against the Twins.
Blue Jays outfielder Travis Snider's home run on Tuesday was his second straight against a left-hander. Before that, Snider had just three home runs in 159 career at-bats against lefties.