The Wanderers had to come from behind to claim their third win on the bounce after Adam Taggart opened the scoring in the fifth minute at CommBank Stadium.
But Hammond equalised with a wonder strike in the 14th minute, then put the Wanderers ahead in the 39th, before Oscar Priestman and Bozhidar Kraev struck in the second half.
With the win over coach Alen Stajcic's former side, the Wanderers sit just a point behind second-placed Western United and third-placed Adelaide, and ahead of Melbourne City on goal difference.
The Wanderers should have taken the lead in the second minute when Zac Sapsford had a tap-in cleared off the line by Josh Risdon.
Three minutes later, Yuto Misao launched a super ball down the left for Lachie Wales, who kept the ball in play then brilliantly cut it back for Taggart to volley home.
Minutes later, the ball skidded out to Hammond at the edge of the area and he beat a defender, cut on to his right boot and unleashed a wonderful strike into the top corner.
Western Sydney took the lead when Taggart lost the ball and the Wanderers streamed forward, with Sapsford launching the ball towards Kraev at the far post.
Kraev's shot bounced off the woodwork, but Hammond was on hand to tap home.
On the stroke of halftime, Lawrence Thomas pulled off a big save to deny Risdon's goal-bound header.
Misao cannoned a fierce strike into the post almost immediately after the break, then clipped the woodwork again less than a minute later.
The Wanderers struck when Oli Sail passed to an under-pressure Luke Amos, whose poor attempted back-pass fell to Oscar Priestman to score.
Western Sydney sealed victory on the counter in the 66th minute, with Sapsford teeing up Kraev to stroke home a fourth goal.
Risdon limped off in the 80th minute and had his right ankle iced.
Both teams aren't in action again until  March 15, when the Wanderers play Melbourne Victory, while David Zdrilic's 11th-placed Perth host Brisbane.
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