Dundee United were sunk in stoppage-time a Tannadice by an Alan Forrest goal that looked suspiciously offside.
It was a shame for home keeper Deniz, who had played so well after being drafted in to replace the injured Benjamin Siegrist.
A fantastic 25-yard freekick from Nicky Clark had put United ahead after 18 minutes but the real hero in the first half was the stand-in goalie, promoted after Siegrist had failed an afternoon fitness test.
The English-born Turk didn’t disappointment, producing a string of excellent saves only to finish on the losing side.
He was beaten first time around on 53 minutes when Jon Guthrie swept home a thoroughly deserved equaliser for Livi but the winner was rather more controversial.
Livi burst forward with the clock ticking down and when substitute Matej Poplatnik squared for Forrest you waited on a flag that didn’t come.
It is not a statistic United fans will want to see but this was only the West Lothian club’s fourth away league win in 40 matches since they returned to the top flight.
However, the Tangerines were sluggish and were beaten by the better side on the night.
The defeat left them down in eighth spot in the table with 11 points out of their 10 matches.
As well as Siegrist’s absence, United also dropped their captain, with Mark Reynolds replaced by the fit-again Mark Connolly in a central defensive pairing with Ryan Edwards. That meant the hosts were skippered by Calum Butcher.
With four minutes on the clock, Scott Pittman had a shot blocked by Connolly as the visitors went on the attack.
United’s replacement goalie Deniz then did well to gather a dangerous cross sent in by Julien Serrano.
The Tangerines were taking time to get going but they were off and running when the lead with a terrific goal on 18 minutes.
Adrian Sporle had won a freekick 25 yards from goal and both Clark and Logan Chalmers stood over the ball. The new Scotland under-21 squad member left it to his more experienced teammate and Clark’s shot landed perfectly, a few inches inside goalie Robby McCrorie’s left-hand post in front of the empty Eddie Thompson Stand.
A wonderful double save from Deniz saved the Tannadice men on 28 minutes, the keeper first blocking Forrest’s strike then tipping Scott Robinson’s follow-up over the bar. It was terrific stuff from the Turkish shot-stopper.
He was United’s hero and he was at it again on 35 minutes when he saved another Robinson shot. Just a minute later, Scott Tiffoney went close with a header for the visitors.
Livi could count themselves unfortunate to be behind and they had another chance five minutes before the break with a long ball from Efe Ambrose reaching Tiffoney but Deniz’s legs got in the way of the strike.
It was a smash-and-grab stuff from United but they still looked satisfied with that as they made their way up the tunnel at half-time.
After the restart, Livingston came close again when Nicky Devlin blasted a ball across the face of the United goal, with Connolly saving the day by clearing for a corner.
The question was: “Could the home team hold on?” The answer came on 53 minutes and it was: “No.”
Guthrie was the scorer, sweeping a shot past Deniz after being picked out inside the box by Marvin Bartley’s pass.
United had to get up the park and put pressure on their opponents for a change.
On 64 minutes, the Tangerines almost opened up Livi when Jamie Robson sent a great pass forward for Clark, who just failed to reach the loose ball before keeper McCrorie.
Devlin headed a corner over as the visitors continued to threaten at the other end, while United made a double change on 75 minutes, with Peter Pawlett and Louis Appere replacing Chalmers and Sporle.
Deniz showed he was still alert on 86 minutes when he saved after Ambrose got on the end of a Forrest freekick.
However, his heart was broken when Livi got their late winner.
He raced out of goal to protest but the goal stood and United were left stunned.
Dundee United: Deniz, Sporle (Appere 75), Clark, Edwards, Chalmers (Pawlett 75), Robson, Butcher, Bolton, Harkes, Shankland. Subs not used: Newman, Powers, Reynolds, McMullan, C Smith, Mochrie, Neilson.
Livingston: McCrorie, Devlin, Ambrose, Guthrie, Serrano, Bartley, Holt, Pittman, Forrest, Robinson, Tiffoney (Poplatnik 76). Subs not used: Stryjek, Taylor-Sinclair, Brown, Fitzwater, McMillan, Lawson, Sibbald, Lokotsch.
Referee: John Beaton.