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11/01/10 7:28 PM ET

Prospecting for gold: AFL auction Saturday

Buster Posey and Mitch Moreland were playing in the Arizona Fall League at this time last year, and they already have home runs in a World Series.

Posey's homer came in the Giants' Game 4 victory. Moreland's came a night earlier for the Rangers, a three-run shot on such an historic Texas day that his bat was sent straight to Cooperstown.

This is becoming a more common scene within Major League Baseball, where this postseason began with 56 percent of the eight rosters comprised of AFL alumni, a total of 112 players. It was 49 percent in 2009 and 56 percent in 2008. Posey and Moreland are examples of why to watch in Arizona.

"I've definitely learned a lot," Posey said after his 2009 AFL stint. "I concentrated on my all-around game. Just facing good competition, whether it's batters I am trying to call pitches to get out or whether it's pitchers I am facing. ... Just trying to figure out what I have to do to be successful."

It can happen that quickly now, the blink of an eye in baseball, and that is why you probably want to pay attention to the MLB.com Auction starting Saturday night. Bryce Harper, the Nationals' No. 1 overall pick from the last First-Year Player Draft, is among many top prospects whose signed game-used items from AFL play are going to be up for bidding, some of it sure to be memorabilia treasures.

This is basically the first shot at signed Harper memorabilia, as he has been making his professional debut with the Scottsdale Scorpions. You will be able to bid on a signed baseball, the lineup card showing him in the No. 7 hole, and you can also get a game-used base that he signed. Get familiar with that autograph, because he hasn't done any real memorabilia signings to date, so this kicks off what could be a long -- and increasingly expensive -- track of Harper collecting.

Harper was hitting .353 entering the week, walloping his first pro homer on Saturday in a 3-for-5 outing. He came a triple short of hitting for the cycle.

"This was a great opportunity to get out here with all the best guys, just get a little taste of pro ball and Minor League ball at the same time," he said. "It's a great experience. I'm just trying to take every game in stride, basically be who I am, get a couple base knocks here and there, just go with the flow. I'm learning a lot of things."

Dustin Ackley was Seattle's first-round Draft pick in 2009, second overall to Stephen Strasburg, and you can get his signed game-used jersey, cap or lineup card with his name. He also signed a baseball with his name and the number 12 after it. You could see him up with the Mariners soon. Hey, the Mariners and Nationals are the only two active franchises never to make the World Series now, so who knows? Maybe he -- or even Harper -- could pull a Posey at this time next year. You just never know, and all you have to do is play the video of Posey's and Moreland's home runs to make the point.

The auction will include signed, game-used items from at least 18 players, including third baseman Josh Vitters (the No. 3 overall pick of 2008 by the Cubs), Eric Hosmer (No. 3 overall pick in 2008 by the Royals), Zack Cox (the Cardinals' 2010 first-round pick and possibly the best pure hitter in their system), Giants first-base prospect Brandon Belt, Yankees outfielder Brandon Laird (the 2010 Eastern League MVP) and White Sox outfielder Jared Mitchell (the 2009 23rd overall pick who played baseball and football at Louisiana State). It's a long list, and anyone who has watched this World Series should have one eye on these kids who could be one short year away from doing the same.

"The Arizona Fall League is proud of its continuing contributions to the development of the sport's most outstanding young players," AFL director Steve Cobb said. "Just nine months ago, players like Ike Davis, Jason Heyward, Chris Heisey, Mike Leake, Buster Posey, Mike Stanton, Drew Storen, Stephen Strasburg, Jose Tabata and many others were polishing their skills in Arizona for the six weeks prior to Thanksgiving, and just months before they became household names to baseball fans across America."

Some of those players, maybe all of them, are just focused on developing pitch by pitch, swing by swing. They might not be thinking about the possibility of doing something profound just one year later on the sport's grandest stage.

"I don't think you ever imagined this," Posey said at his locker after his Game 4 homer, after catching Madison Bumgarner's shutout. "If you do that back then, you're getting a little ahead of yourself. You're trying to take little steps and keep improving."

Mark Newman is enterprise editor of MLB.com. Follow @MLB on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.