Scotland international midfielder Dorrans sealed Albion's success with a 75th minute penalty, having also earned them a 3-2 win at Blackpool from the penalty spot last month.
The victory, Albion's fifth successive Championship success at The Hawthorns, moved them a commanding five points clear of third-placed Nottingham Forest.
They had to do it the hard way against play-off chasing Blackpool, who had made the perfect start through Charlie Adam.
The Scotland international gave Blackpool a sixth-minute lead with his 14th goal of the season.
Their advantage lasted only seven minutes when Ishmael Miller, who was making his first start in 15 months after recovering from cruciate knee ligament damage, fired Albion back on to level terms.
Robert Koren's second successive long-range special in the 53rd minute looked to have ended Blackpool's challenge.
But substitute Brett Ormerod equalised just two minutes after being sent on, only for Dorrans to then leave Blackpool with no way back.
Blackpool, who have now failed to win any of their last six away games, stunned Albion when Adam was picked out by David Vaughan and he let fly from 30 yards with a low drive that beat Scott Carson before flying in to the net off the foot of the post.
Adam was unfortunate not to grab a second three minutes later and that let-off sparked Albion into life with Steven Reid seeing his 12th minute header cleared off the line by Keith Southern.
But it was only a brief let-off for Blackpool and they were pegged back 60 seconds later when Chris Brunt released Miller, who slid his shot under Matt Gilks from eight yards.
Blackpool were then fortunate not to fall behind in the 28th minute when they had three let-offs in the space of a few seconds.
Jonas Olsson headed Dorrans' free-kick against the post, Miller's follow-up was saved by Gilks before Reid blazed over the bar.
Miller then squandered another golden chance to put Albion in control when he headed a James Morrison cross wide from just six yards in the 34th minute.
While Albion were dominant in terms of chances created in the opening period, Blackpool still carried a threat on the break and Southern came close to regaining the lead for them when his rising drive was tipped away by Carson five minutes before half-time.
That was a vital intervention by Carson and Koren cashed in when he collected a pass from Dorrans.
Slovenia midfielder Koren cut in from the left wing and left Gilks grasping at fresh air with a rising 25 yard drive - a carbon copy of his winning goal in the previous game against Sheffield Wednesday.
Any hopes Albion had of cruising to victory were then dashed by Ormerod who met a cross from Adam to head home his eighth goal of the season in the 72nd minute.
But Blackpool did not have a chance to try and build on Ormerod's strike as Dorrans converted his 14th goal of the campaign from the penalty spot three minutes later after Joe Martin had fouled Giles Barnes.