If only he could always play against his old team, LaRoche really would be the star many thought he’d become. The 26-year-old third baseman went 5-for-5 with two homers, two doubles and six RBI in Monday’s rout of the Dodgers. That made him 14-for-29 against the Dodgers this season. His slash line is .483/.516/.931, compared to .259/.333/.403 overall. LaRoche’s performance this month and in the four-game series win over the Dodgers in particular won’t change the fact that he’s been a disappointment in his first full season as a regular, but it likely will lock up a starting job for him in 2010. He’s hit .338 and launched five of his 12 homers during September. Beyond the first couple of months of next year, it’s hard to tell what’s in store. The Pirates’ former top position prospect and current top prospect are both third baseman. Neil Walker, though, needed a strong finish just to end this year with a modest .264/.311/.480 line as a 23-year-old in Triple-A, and Pedro Alvarez seems increasingly likely to end up at first base. LaRoche looked like a future 30-homer guy in the low minors, but injuries sapped his power potential. Almost as disappointing is that his on-base skills haven’t come along. LaRoche posted OBPs of .410, .399 and .445 in his final three minor league seasons. He was often aided by kind offensive environments, but his patience and his ability to hit line-drive singles and doubles figured to make him a quality major leaguer. Instead, he’s really only been adequate against left-handed pitchers so far. Fortunately, two-homer, two-double games do have a way of changing numbers in a hurry.