Ifill - not for the first time - found space out wide and curled in a perfect cross from which unfortunate Adelaide defender Nigel Boogaard produced a perfect diving header into his own net. Boogaard felt the pressure of Sigmund, who was breathing down his neck having charged forward into the area.
Earlier, Adelaide could have sealed the game with 10 minutes to go but Dario Vidosic couldn't find an unmarked Bruno Djite in the six yard box.
There was plenty of purpose and passion from the Phoenix but a noticeable lack of precision. The home side dominated territory and shaded possession but, until the introduction of Ifill, there was no one to provide the vision and movement on or off the ball.
Too often the final pass went astray, or was just a hopeful pass played into space that the Adelaide defence, marshalled superbly by their captain, Socceroo and former Phoenix defender Jon McKain dealt with easily.
Adelaide in contrast looked good on the ball. Their triangles were well constructed and concise; the Phoenix's looked made in Bermuda. For all that, Adelaide were perhaps fortunate to take a 1-0 lead into the break.
Bruce Djite's brave toe poke in the 45th minute capped a clever passing move, but Tony Warner had barely been employed in the Phoenix goal. The ex-Millwall keeper will take some blame for the goal, as he was caught on his heels; slow to come off his line to challenge Djite.
The Phoenix created a hatful of chances, mostly from Manny Muscat and Leo Bertos angled deliveries into the box; the best fell to Chris Greenacre in the 43rd minute but he dropkicked over the bar from six yards.
On this evidence, it is hard to see how the Phoenix can wait until January for a new striker. Greenacre, who covered every blade of grass on the park, toils manfully up front but needs a foil beside him. The return of Ifill will help.
There is also a lack of attacking presence in midfield, with Vince Lia, Tim Brown and Nick Ward providing more industry than imagination. Lia, in particular, struggled in his first game back from injury and picked up a needless yellow card, his 21st in 65 A League games, almost one every three matches.
Ifill's entrance changed the game. A deft turn, an angled pass, a sharp dribble; suddenly the Phoenix seemed to have an attacking threat and could create some uncertainty in the Adelaide defence.
"It was nice to get a point and have a hand in the goal," said Ifill. "I feel great now and it is encouraging. They were good value for the point but we need to put our chances away - that has been the problem in the last few weeks."
Ifill was also impressed that 20,000 had turned up to a rugby stadium.
Wellington Phoenix 1 (N. Boogaard own goal 83), Adelaide United 1 (B. Djite 45). Halftime: 1-0
