The City striker broke the deadlock on the stroke of half-time when Danny Tiatto's shot was beaten away by the keeper and in rushed Hammond to sweep home the loose ball.
And the Foxes doubled their advantage on 52 minutes when Stephen Hughes crossed from the right and man of the match Levi Porter stepped inside defenders Neil Austin and Bobby Hassell to fire home from close range off the underside of the bar.
The Tykes had arrived in the East Midlands on a high having gone four games unbeaten since caretaker manager Simon Davey took over from the sacked Andy Ritchie last month.
But they were ultimately swept aside by the rampant Foxes who produced what their manager Rob Kelly described as their best performance since he took charge at the Walkers Stadium.
But it might have been all so different had Barnsley made their first-half chances count. On the half-hour mark the Tykes almost unhinged City when Kyel Reid slipped beyond Richard Stearman and crossed to the far post where the unmarked Leon Knight headed across the face of goal and against an upright.
Then, after Hammond had headed over from close range, Paul Henderson came to his side's rescue when he dived to turn away Reid's goalbound shot.
On 39 minutes Hughes rattled the Barnsley post from 20 yards before Henderson had to be at his best to claw away a Daniel Nardiello free-kick and, moments later, Nardiello went close again when he headed a Reid corner narrowly over.
That was as good as it got for Barnsley who, after City's goals either side of half-time, were strictly second fiddle.
But for all their domination City failed to add to their tally with Hammond, right at the death, sprinted clear of the final defender before seeing the keeper claw away his goalbound drive.