The Reds found the net through Ryan White on 73 minutes, before Daniel Wilmering ensured the home side took a share of the spoils with a goal in the 94th minute at McDonald Jones Stadium on Saturday.
Top-of-the-table Newcastle move three points clear of second-placed Auckland FC with two games remaining, following Auckland's 2-2 draw with third-ranked Melbourne Victory earlier in the day.
United leapfrog Victory, a point clear in third place.
Chances were few and far between in the first half. Adelaide's Jonny Yull had a great chance midway through the first period after he was released by Luka Jovanovic, but he scuffed his shot with just James Delianov to beat.
Zavier Bertoncello struck the upright on 42 minutes after he was teed up by Zach Clough. The first-time left-footed curler was deflected off Ethan Alagich, before hitting the outside of the woodwork.
Newcastle dominated the earlier stages after the interval but could only create a series of half-chances.
On 64 minutes, Adelaide had a great chance with a cross from substitute Brody Burkitt wide on the right.
It was only half-cleared by the Jets, allowing Ryan Kitto to control the loose ball and volley towards the bottom corner, forcing an impressive diving save from Delianov.
The hosts had a glorious opportunity on 72 minutes to break the deadlock. Clough threaded a delightful through-ball for substitute Lachlan Rose, who just had goalkeeper Joshua Smits to beat.
He fired his shot directly into the Dutch custodian and was left to rue the missed opportunity as the Reds found the net almost immediately on 73 minutes.
Substitute Anselmo collected the ball in midfield and split the Jets' defence, picking out White, who rounded Delianov and slammed the ball home from close range.
Two minutes later Anselmo thought he had his second assist. The Brazilian latched on to a ball over the Jets' defence and drove a cutback to the top of the box for Alagich to slot home, but it was ruled out by VAR, with the ball judged to have crossed the byline before Anselmo's cross.
Anselmo then put the ball in the net with an acrobatic bicycle kick after a cross from Yull, but it was ruled out for offside.
Newcastle would have the last say, with Wilmering tapping in from close range almost four minutes into stoppage time.
Eli Adams drove a low, hopeful ball into the packed Reds' penalty area. It evaded everyone and forced Smits into a diving save, with the rebound sitting perfectly for Wilmering to turn in.
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