OAKLAND – The beauty of baseball is that some momentous events cannot be explained.

This one, for example: Oakland Athletics, American League West champions.

It happened here on a luminous afternoon of primal emotions for a city and a fan base that didn't believe in the wonder of its local nine until the boys on the field morphed into something extraordinary.

With the lowest payroll in baseball and stocked with players who very recently wore River Cats jerseys and played along the banks of the Sacramento River, the A's pummeled the powerful Texas Rangers 12-5 on Wednesday to win the division.

In the process, the A's topped the Rangers and the Los Angeles Angels – both teams with payrolls more than double that of the A's. Beginning Saturday, the A's join the postseason elite, taking on the Detroit Tigers. Detroit also has a payroll that dwarfs Oakland's, but no one seemed too worried about that Wednesday.

"Everyone in this clubhouse feeds off each other," said Rick Rodriguez, who spent 10 years as the River Cats pitching coach before becoming bullpen coach for the A's.

That team chemistry is a major factor in the A's having exceeded expectations in a year that started with many in the media pegging them to finish dead last.

The A's have been the best team in baseball since early June. But until recently, they drew little notice because everyone assumed they would trip up. Wednesday marked the only time during the team's critical three-game series with Texas that the stadium sold out.

They surged regardless, and now everyone asks – how?

Players such as Grant Balfour, the tightly wound Aussie closer who recorded Wednesday's final out, repeated a refrain common to A's players: "We're not intimidated. We knew how good we were."

But how? Why?

This Oakland team – which by the end of the season had five rookie starting pitchers – won 94 games. They set an all-time record for most wins by any team with rookie starters.

They did it despite losing their best pitcher, veteran Bartolo Colon, due to a suspension for performance-enhancing drugs. Their other leader, pitcher Brandon McCarthy, ended the season prematurely after he was struck in the head with a line drive and was rushed to a hospital with a skull fracture.

The best-known player in the organization at the beginning of the season was Manny Ramirez, the disgraced steroid star who never made it past the River Cats.

They lost Brandon Inge, their veteran third baseman, and only got better.

Each time, the A's got younger and inserted a different River Cat into a different key role. Their third baseman, Josh Donaldson, is trained as a catcher. Sean Doolittle, a key reliever, only recently started pitching.

Second baseman Cliff Pennington is a natural shortstop. Yoenis Cespedes, their star player and a Cuban defector, doesn't speak a lick of English. Cespedes had never played big-league ball before this season. He came through Sacramento earlier this season while coming back from an injury.

All of these men, along with Brandon Moss, Chris Carter, Seth Smith and Derek Norris, were recent River Cats who joined players such as Josh Reddick and Coco Crisp to propel the A's to this moment. In all, 24 of the team's members played with the River Cats at some point this season.

On Wednesday, Moss, the first baseman, had three RBIs. Smith, the designated hitter, had one. Norris, the catcher, hit a home run.

"I think our most valuable player was the Sacramento River Cats," said general manager Billy Beane in a champagne-soaked A's locker room filled with delirious players.

A big-league team that so closely resembles its Triple A affiliate is not supposed to do what the A's have just done. In a 162-game season, the only day the A's secured sole possession of the lead in the American League West was the last. They won their last six games, eight of their last nine and went 51-25 in the second half of the season. The players mentioned above were the reasons the A's went from scoring the fewest runs in the American League in the first half of the season – to scoring the most in all of baseball in the second. They also hit the most home runs in the second half.

Beane, whose low-budget use of statistical analysis to find undervalued talent became the focal point of the book and film "Moneyball," was asked how he did it.

The normally tightly controlled Beane broke into a goofy grin. But even he, the baseball genius, seemed at a loss to deconstruct what's become the best story in baseball.

"We've done some pretty amazing things over the years, but this was pretty unbelievable," Beane said. "Even I ask, 'How did they do that?' "

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