Mountcastle went 2-for-5 with a solo home run in Sunday's 22-7 loss to Toronto.
The 24-year-old went deep in the third inning, but even with his homer, Baltimore trailed 16-4 at the time. Mountcastle has been excellent in his first full major-league season, slashing .264/.316/.498 with 28 long balls, 79 RBI, 68 runs scored and four stolen bases through 507 plate appearances. He's gone yard in three of his last five contests.