The 20-year-old right-hander allowed two hits and struck out five over five scoreless innings Tuesday as the Salem Red Sox edged the Lynchburg Hillcats, 2-1.
Through two appearances in 2010, including a rain-shortened season debut, Pimentel has allowed only three baserunners and has yet to surrender a run.
He finished strongly against the Hillcats. After allowing back-to-back one-out singles in the second inning, Pimentel retired the last 11 batters.
Since signing with Boston as a non-drafted free agent in 2006, the native of the Dominican Republic has been named the Red Sox's Minor League Latin Program Pitcher of the Year and a New York-Penn League All-Star. But it wasn't until last year that Pimentel started landing on lists of the organization's top pitching prospects.
A year ago at Class A Greenville, he struck out 103 batters and walked only 29 over 117 2/3 innings.
Pimentel's fastball can touch 93 mph and he also throws a cut fastball, curveball and changeup.