The home side dominated possession throughout the first half and enjoyed numerous chances on goal before they finally got on the board when the Phoenix were awarded a penalty of their own.
Brazilian winger Daniel hammered the ball home past Sydney goalkeeper Liam Reddy to draw the sides level.
Daniel then turned provider in the 42nd minute when his well-timed pass put Sanchez in to space and the impressive Spaniard produced a classy finish to give the Phoenix the lead.
The sides went in to the break after a frenetic first half with the Phoenix ahead 2-1, although Sydney managed to rattle the post and crossbar during the opening 45 minutes.
Reddy, who returned to his old stomping ground after playing for the Phoenix two seasons ago, looked nervous throughout the game and flapped at a few crosses and corners in an unconvincing display between the sticks.
The Phoenix came out in the second spell and enjoyed plenty more possession but failed to extend their lead and Sydney equalised through Bruno Cazarine in the 64th minute when his shot squeezed under Phoenix custodian Tony Warner.
As the Phoenix pushed in search of a winner Leo Bertos provided a pinpoint corner for Sigmund to latch on to and the popular defender headed home in the 78th.
Ifill, who returned to the side from injury then added a fourth in stoppage time to push the Phoenix in to fourth on the A-League ladder.
The game was part of the A-League's "Big Wednesday", which sees all teams play back to back during the day and the Phoenix checked in with a strong home crowd of 8411.
Wellington Phoenix 4 (Daniel 25' pen, Dani Sanchez 42', Ben Sigmund 78', Paul Ifill 90') Sydney FC 2 (Brett Emerton 16' pen, Bruno Cazarine 64') HT: 2-1