Four years ago today, the Oakland A’s stood in third place in the AL West with a record of 38-42, 21 games behind the suddenly explosive Seattle Mariners. With names like Jason Giambi, Miguel Tejada, and Eric Chavez filling the lineup card, and Tim Hudson, Mark Mulder, and Barry Zito in the rotation, the A’s were suitably disappointed with their tepid start, and responded with a monster second-half run.

From July 1 through the end of the season, the A’s ran the table with a 64-19 record, which wasn’t enough to catch Seattle, but placed them comfortably in the wild-card slot. It was just one in a series of great second halves for Oakland, which played .600 ball or better in the second half of each season from 2001-03, making the postseason each time.

Why is this important? As of yesterday, the A’s stood in third place in AL West with a 38-40 record. This time, however, they are just 11 games behind the Angels and look poised to begin another successful second-half run. With a record of 19-8 in June and seven straight wins, the A’s have gotten off the mat and at least started to justify the expectations of those among us who thought the midwinter trades of Hudson and Mulder wouldn’t prevent them from having a successful season.

You might recall that the A’s 17-32 start was caused in large part by an offense as dysfunctional as you’re likely to see. For the season’s first two months, the A’s ruined their sparkling walk rate and strikeout-to-walk ratio with a complete lack of any other offensive assets. They didn’t hit for average, drive the ball, or run the bases, leaving them with one of the game’s worst lineups, last or next-to-last in the AL in virtually every offensive category.

This month, however, the A’s have begun to hit for average and power, enabling them to leverage the strong walk rate and plate discipline – 85 walks against 96 strikeouts in June – into runs. The A’s have scored 136 runs this month, good for a spike in their per-game average from 3.94 to 5.44 runs a game. One huge difference has been the long ball; after hitting 28 home runs in April and May combined, they’ve matched that number in June. It’s the difference between an offense that can’t win and one that can.

Most of the gain is simply regression to the mean: Eric Chavez and Jason Kendall weren’t likely to remain the below-average hitters they were in the season’s first two months. Going into yesterday’s play, Chavez had hit .385 AVG/.449 OBA/.719 SLG in June, having posted a 239/.276/.321 mark in May. Kendall, who hit .234/.314/.298 in May, has found his singles, if not everything else: He’s hitting .314/.410/.349 in June. The return of Bobby Crosby has also been a big boost, as the second-year shortstop has hit .318/.375/.523 this month.

Those three players are responsible for most of the A’s offensive improvement in June, although nearly everyone on the roster has started slugging at a higher rate. The support players – guys like Scott Hatteberg, Bobby Kielty, and Mark Kotsay – look a lot better when they’re the fourth-, fifth-, and sixth-best hitters in the lineup rather than the best three, as was the case for the first third of the season.

The bump in runs scored would be enough to explain the turnaround, but the A’s have also done a better job on the other side of the ball. The rotation, which itself went through an awful stretch in May, has righted itself to become a consistent producer of quality outings. Joe Blanton, who was arguably the worst pitcher in baseball last month (28 runs, 31 hits, 14 walks, six strikeouts in 18 1/3 innings), has posted a 28/9 K/BB and 2.06 ERA in 43 2/3 innings this month. Rich Harden, back off the disabled list, has picked up where he left off, with one run allowed in two six-inning starts. Zito may never get back to his 2002 peak, but he’s settled into being a good mid-rotation starter. Even Kirk Saarloos is enjoying a revival with a 2.08 ERA (and 2.42 K/9) in June.

And then there’s the guy they got for Mulder. Dan Haren has a 27/5 K/BB and a 3.11 ERA in June, and is at 78/32 for the season in 104 innings. After a May wobble, he’s established himself as the A’s second-best starter behind Harden. How do his numbers this season compare with those of the more famous pitcher in the deal?

Haren’s nine unearned runs allowed make the ERA difference less meaningful than it appears at first glance. But on second glance, Haren has a meaningful edge on Mulder in runs, in underlying indicators, and in advanced metrics. He’s outpitched Mulder so far, giving the A’s the edge before considering any of the other players – or any of the money saved – in that deal.

It’s important to remember that this isn’t 2001. The A’s aren’t as good as they were then, and the competition for the wild card is stiff this year. Oakland is just five games behind Baltimore, but they’re behind seven other teams, including the Twins – who are almost certainly the best of the bunch.

In truth, these A’s look less like the 2001 team than the 1999 version. That was the year the A’s moved from rebuilders to contenders. With the team in both the division and wild-card races in midsummer, GM Billy Beane straddled the line between mortgaging the future and making a run, completing four trades that didn’t quite put the team over the top in ’99, but brought in new faces who would contribute to playoff teams in 2000 and beyond.

That’s where the A’s find themselves again, in the gray area between rebuilding and contending, and with a future that should look much better than their present. The challenge for Beane is to straddle that divide as well as he did in 1999. This could mean trading away Zito, a move that would look a lot worse for the A’s – due to Zito’s Cy Young reputation – than it actually would be.

What’s certain is that the A’s aren’t just a footnote to this season. While they’ll have trouble winning 90 games again, Beane’s underlying idea – that the team can contend during a transition period – seems to be sound. The Braves are the model for successful roster turnover; if the A’s can pull it off, they would be the first small-market team to achieve this feat, setting off another round of agitated debate over the right way to run a baseball team.

Mr. Sheehan is a writer for Baseball Prospectus. For more state-of-the-art commentary, visit baseballprospectus.com.