You couldn't ask for a more immediate impact from a September call-up than what Brandon Allen did for the Arizona Diamondbacks on Wednesday.

I was there to watch Mat Latos versus Barry Enright, and despite Latos tying a career high in strikeouts, Allen was the story of the game.Blocked at first base this season by Adam LaRoche, Allen split time between first base and left field at Triple-A. He made a good first impression in left field Wednesday, making a Web Gem-like catch with one foot on the fence in the left-field corner. He also made another fine defensive play later in the contest. Oh yeah, and one more thing: He hit the game-winning grand slam.After Allen made the first catch, my friend Joe Sheehan of the Joe Sheehan Baseball Newsletter immediately e-mailed me, asking whether Allen had lost a bunch of weight and expressing surprise that Allen was able to make the play. To be honest, I was surprised as well. Allen is indeed a little trimmer and seemingly more fit, which likely has helped his transition to the outfield. More importantly, the club has worked on Allen's hitting stride since last season, getting him back to his older approach of having a narrower setup and taking a stride forward in his swing, as opposed to a very wide stance with little to no stride. The change gives him a little more balance, consistency and a better chance of handling good left-handed pitching. Allen hit 25 homers with an on-base percentage better than .400 at Triple-A this year, and he has a chance to provide you with some power if you can cover for what likely will be a low batting average.With Gerardo Parra providing little offensively this season, look for the 24-year-old Allen to get a good amount of at-bats down the stretch, even after Justin Upton returns from injury. Consider him an NL-only sleeper for these final few weeks of the season.

Assessing the September call-ups