Liam Rosenior was also on target at the KC Stadium on Saturday as the Tigers opened up a bit more breathing space between themselves and the drop zone and kept the Baggies looking anxiously over their shoulder.
Steve Bruce's side, who are now eight points clear of the bottom three, opened the scoring on 32 minutes as Rosenior diverted a diving header past an unfortunate Ben Foster after the Baggies goalkeeper had kept out a penalty from Nikica Jelavic.
Long, who earned that spot-kick, then got in on the act six minutes later as the visitors failed to deal with a corner from the left and, after Jake Livermore hooked back into the box, the ball was touched on for the Republic of Ireland international to volley into the bottom corner.
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, Curtis 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 Graham 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 Pepe 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 wrestled total control.
First David Meyler sent a header from a Tom Huddlestone corner inches wide of Foster's upright before Long crumbled under Craig 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 minutes later which was superbly tipped over the bar by Foster, before Long made it 2-0 in the 38th minute when a looping 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 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.