Both sides started the game level on points, but Peterborough's defence made sure that goalkeeper Joe Lewis was well protected as the Cumbrians failed to score in front of their own fans for the third successive game.
Midweek hat-trick hero Gary Madine missed Carlisle's best chance in the second half, but clear-cut chances were hard to come by.
Carlisle were unable to get into the game and it was Peterborough who grabbed a 32nd-minute lead when Aaron Davies won possession just inside the Carlisle half and his through-ball enabled Mackail-Smith to race clear of the defence and coolly slip the ball past goalkeeper Adam Collin from just inside the box.
Mackail-Smith, with a shot that lacked the power to beat Collin, and Boyd, with a low drive into the side netting, had chances to increase Posh's advantage before half-time.
A double substitution at half-time, which saw Craig Curran and Oliver Norwood introduced, produced a more attacking threat for Carlisle, while Madine should have done better with a 77th-minute header from close range when Frank Simek picked him out with an accurate cross.