It seemed as though the Phoenix had barely finished celebrating Sigmund's powerfully struck 79th-minute header before the sides were back on level terms after Chianese netted in the 80th and 82nd.
Cue Ifill.
The Englishman, who played more than 200 games for Millwall and also turned out for Crystal Palace and Sheffield United previously, pushed forward and was taken down in the box by the Sydney defence.
It was a clear foul and the referee pointed to the spot to give Ifill the chance to reclaim the lead for the home side.
The 32-year-old made no mistake, much to the delight of the 10,019 people who were on hand to witness the Phoenix's first home playoff game since 2010.
Ifill, who had been denied at least two clear penalties during the A-League's regular season, said it was great to get the opportunity to convert one in a big game.
``I've sort of wanted one for a long time, but with four minutes to go in an elimination game was a bit nerve-racking and they were doing their best to put me off and I sort of took a long time,'' Ifill said.
``It's nicer when you can just put the ball down and put it in the back of the net. I don't like the waiting round. But at the end of the day I stuck it in the net and we got one so I'm pretty pleased.''
Ifill said the three-minute frenzy where Sigmund and Chianese scored their goals was a blur.
``I didn't have time to even think about it. It seemed like their two goals and our one were within about a minute. It was just surreal. At 2-2 they must've thought, `right we are back in this' and in the ascendancy and for us to get a penalty must be gut-wrenching for them. To be honest I thought they were very good tonight, they were hard to break down.''
Brown, who announced during the week he would retire at the end of the season, was given the captain's armband for the night in place of regular skipper Andrew Durante and it galvanised the Wellingtonian who put in a strong performance.
The Phoenix face the prospect of a trip to Perth next weekend to meet the Glory or they could host Melbourne Heart if the Victorians can upset the men from Western Australia on Sunday.
Wellington Phoenix 3 (Tim Brown 47', Ben Sigmund 79', Paul Ifill 86') Sydney FC 2 (Joel Chianese 80', 82') HT: 0-0|
Follow Daniel Richardson on Twitter