Chris Millar scored his first goal in nearly four years to give St Johnstone a dramatic comeback win at McDiarmid Park.
Calum Butcher put United into the lead in the first half, and it wasn’t until the 76th minute that Saints equalised through Michael O’Halloran his sixth league goal of the season.
Then, with just three minutes left, Millar found the net for the first time since March 2011 to secure Tayside derby victory for the Perth men and extend their unbeaten run to eight matches.
Both sides had long-range efforts in the early stages.
John Rankin dragged his 20-yarder wide of the target, but Lee Croft forced a diving tip over the bar from Rado Cierzniak.
From relatively promising beginnings to this game, a stalemate ensued.
It took until the 30th minute for another attempt on goal, and this time it was Michael O’Halloran. He struck his angled shot well, but Cierzniak had his near post covered and it went into the side-netting.
United eventually made Alan Mannus put his hands on the ball but Jaroslaw Fojut’s 37th-minute back post header never looked like beating the Northern Irishman.
Saints came close to breaking the deadlock on 40 minutes.
Chris Millar picked out Dave Mackay on the over-lap down the right and he squared the ball inside, where Steven MacLean thought he was about to get a simple finish from six yards out. However, Callum Morris timed his interception perfectly to thwart the comeback striker.
The Morris cut-out proved to be an even bigger moment three minutes later when United took the lead.
Butcher delivered the sucker-punch with a low finish past Mannus into his bottom right corner.
The teams traded near things after the re-start.
Mackay cut in from the left and Cierzniak’s save from the Perth skipper’s 22-yarder was an excellent one.
Moments later Stuart Armstrong narrowly missed the target with a shot from inside the box.
United should have been 2-0 up on the hour mark. Nadir Ciftci held off three Saints players in the corner of the pitch. He then delivered a perfect cross for Blair Spittal, who missed the target with a header from six yards out.
The Tangerines were looking pretty comfortable, but Saints produced an equaliser on 76 minutes.
Croft crossed to the back post where O’Halloran was unmarked and his downward header gave Cierzniak no chance.
The United bench were furious with referee Alan Muir as they believed Mackay had handled the ball in the build-up.
Saints were sniffing a winner and a Brian Easton shot was tipped round the post and from the corner, MacLean scooped the ball over the bar.
A United defence that had looked so composed earlier in the game was now creaking, and the home winner arrived on 87 minutes.
Millar worked the ball on to his right foot and curled his shot into the far corner before he was mobbed by his team-mates at the corner flag.