John Aloisi's United entered their penultimate game two points behind Melbourne City and one behind Melbourne Victory, who have just one game left.
They realistically had to beat the Jets, given leaders City were in action against wooden spooners Perth Glory on Wednesday, to have a shot at silverware before the final round.
Things were on track when Adisu Bayew scored in the 27th minute but several missed opportunities, then Jordan Elsey's 52nd-minute header, meant United only claimed a draw.
Wednesday's result also opened the door for Melbourne Victory, who are level with United on 45 points to snatch a top-two spot.
United snatched the lead at McDonald Jones Stadium when Neil Kilkenny burst forward through the Jets defence before squaring.
Aleksandar Prijovic let the ball go, aware he could be offside, and Bayew tapped home.
Newcastle almost equalised on the counter in the 37th minute when Sam Silvera tried his luck with a fierce shot from just behind the halfway line.
Jamie Young got back just in time to make an outstanding one-handed save.
Lachie Wales blasted just over the bar in the 40th minute.
Then Newcastle goalkeeper Michael Weier stepped up, denying Kilkenny in the 44th then pulling off an extraordinary one-handed save to stop Connor Pain a minute later.
Seven minutes after the break, the Jets struck.
Silvera looped in a wonderful corner and Elsey leapt highest at the back post to head home.
Newcastle should really have won from there with Beka Mikeltadze and Silvera hitting the post in the 62nd and 74th minutes respectively while Young denied Lucas Mauragis in the 68th.
United's night was further soured by substitute Dylan Pierias limping off in the 70th, while they had earlier confirmed Steven Lustica (calf) would miss three-to-four weeks.
