Long lifted his new club Hull to the brink of safety by winning the controversial first-half penalty which led to their opening goal, then turning in a Curtis Davies' flick-on seven minutes before the break to seal a solid 2-0 win for the Tigers.
Long, who scored 22 goals in 87 appearances for West Brom before his surprise sale in January, was barracked mercilessly by the massed ranks of visiting fans for his part in the penalty incident, in which former team-mate Craig Dawson appeared to make minimal contact.
Justice looked to have been done when Ben Foster guessed right to block Nikica Jelavic's penalty - only to flap the ball straight at a grateful Liam Rosenior, who headed home his first senior goal since October 2009.
With Long also coming close when he lashed a long-range effort against the post in the second half, the increasingly nervous visitors were left to reflect on how much brighter their season might have been if the Ireland international had still been wearing black and white stripes.
Those two goals in eight first-half minutes shattered the mood of cautious optimism which had hung over the Baggies after boss Pepe Mel eased some of the pressure with his first win in charge at Swansea last week.
The opening period promised much, with Stephane Sessegnon firing a first minute effort over the bar before the visiting supporters staged a minute's silence in honour of their former striker Jeff Astle, whose family this week launched a 'Justice For Jeff' campaign, calling on the FA to launch research into the effects of heading leather footballs.
The hosts belatedly stirred, Davies hitting a goal-bound effort in the 16th minute which clattered the legs of Youssouf Mulumbu, but the visitors were still threatening with swift counter-attacks and Graeme Dorrans came closer two minutes later with a swinging volley which was well saved by Tigers keeper Allan McGregor.
Davies denied Victor Anichebe with a crucial saving challenge in the box as Mel's men continued to look more likely to break the deadlock, but the momentum changed in a 10-minute period starting just before the half-hour mark in which the Tigers wrested total control.
First David Meyler sent a header from a Tom Huddlestone corner inches wide of Foster's upright before Long crumbled under Dawson's challenge in the box and won a penalty from referee Chris Foy.
Video replays suggested the decision was harsh and justice looked set to be served after Jelavic's poor penalty, but Rosenior was in the right place at the right time to open the scoring.
Huddlestone fired a long-range rocket eight minutes later which was superbly tipped over the bar by Foster, before Long made it 2-0 in the 38th minute when Jake Livermore's long ball into the box was flicked into his path by Davies.
In a much more low-key second period, Jelavic flashed a low shot just wide from a Sone Aluko cross but the hosts were warned against complacency when McGregor had to be alert to block Victor Anichebe's powerful header,
Long almost increased his former club's torment on 67 minutes when he picked up a cross-field pass from substitute Robert Koren and curled a right-foot effort from long range which came back off Foster's right-hand post.
As a filthy rainstorm closed in on the KC Stadium, Long's productive day against his former club came to a premature end in the 77th minute when he limped to the touchline and was replaced by Stephen Quinn. But by that point his job was done.