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On Tuesday the Athletics and Yankees began a three-game series sure to evoke the words "potential playoff preview." Both teams made last year's tournament and, through two-plus months of the season, are positioned to attend this year's dance, with the American League's third- and fourth-best records. The Yankees owned a slight edge, yet those who put stock in recent success might favor the A's. Oakland has won nine series in a row while tallying a 20-5 record since their last series loss.

The middle of June is when small-sample size concerns dissipate, to a degree. Everyday players march toward 300 plate appearances while teams near the halfway point in the schedule. But there is still plenty of noise in mid-June numbers, and the noise is ominous for the A's: when considered against their schedule thus far, the A's have yet to prove they're an elite AL team.

There are a few generally accepted truisms about playoff teams. One is they win their home games. Another is they win games against inferior teams. Ergo, they should really win their home game against lesser foes. The A's are living up to those expectations across the board. They can boast about one of the top home records in the majors. Likewise, they own the best record against sub-.500 teams in the AL. However, Oakland's work against better competition, like the teams it would face in October, leaves a lot to be desired. Entering the Yankees series, no winning team in the AL had a worse record against winning teams. (With wins in the first two games of the series, the A's have now pulled ahead of New York.)

Breaking a team's season down into chunks is always a dangerous and often a mendacious exercise. Take Oakland's 22 games against bad AL teams—the Astros, Angels, and White Sox—and compare with their other 45. A comparison shows that almost half of Oakland's overall wins have come against bottom-feeders, as they've gone 19-3 against those weaker teams—including 9-0 against the Astros—and 21-24 versus everyone else. The contrasting records are supported in the Athletics' runs scored and allowed averages. Oakland has scored more than six runs and allowed fewer than four runs per game against the bad teams, while scoring fewer than four and allowing more than four against the good teams.

As the season burns on Oakland's record against good teams could even out. But consider the alternative: The A's issues endure through the regular season. Is it possible that Oakland could still make noise in the postseason, and bring home their first world title since 1989? Or are regular-season difficulties against good teams portent of a quick exit in October?

Say the A's continue on this pace for the rest of the season and still make the playoffs. Their gap in winning percentage against good and bad teams would then become the third-largest among postseason teams since the 2008 season, trailing the 2010 Reds and 2011 Brewers. A's fans hoping for a World Series title can point to their Bay Area rivals, the Giants, as proof it can happen. After all San Francisco posted the third-largest differential during their World Championship-winning 2010 season. They aren't the only wins to shift gears once the playoffs started: The 2008 Phillies also won the World Series following a sub-.500 season against winning teams.

Postseason Teams with Biggest Win Percentage Differentials, 2008-2012

Team

Season

Win % v. < .500

Win % v. >= .500

Differential

CIN

2010

65.1%

37.7%

27.4%

MIL

2011

68.3%

44.3%

24.0%

SFN

2010

67.0%

44.6%

22.4%

BOS

2008

71.9%

50.0%

21.9%

MIL

2008

67.1%

46.1%

21.0%

Of course the schedule itself is no fault of the A's, who just so happen to share a division with two of the weaker AL teams to date. If anything, Oakland should be commended for taking advantage of a fortuitous schedule, which has seen them play the Astros more than any team save the Angels—who, conversely, own a 3-7 record against the AL's worst team. Besides, the schedule is a zero-sum game, and the A's will have fewer games against the Astros heading forward than the Rangers, a factoid sure to impact the division race.

Playing better against bad teams is an anticipated reality; it's just the split that make Oakland stand out. At the same time, a series win against the Yankees, and some of the other finer teams in the league, would go a long way to validating the A's status as an elite AL team.

A version of this story originally appeared on ESPN Insider Insider.