GOALS either side of the break from Simon Cox and Roman Bednar saw already-promoted Albion equal their best-ever points haul for a season.
Cox's stunning opener in the second minute of first-half stoppage time and Roman Bednar's close-range strike in the 55th minute - both their 11th goals of the term - underlined the Baggies' supremacy.
This ninth successive home win also moved Roberto Di Matteo's men onto 89 points, matching the tally set by Gary Megson's promotion-winners in 2002.
Any fears the players' minds would be distracted by the fact it was already a case of 'job done' evaporated from the first whistle as the hosts produced a committed performance to run out comfortable winners and complete their eighth double of the season.
Albion's eighth win of a ten-match unbeaten run also moved them a massive 14 points clear of one-time challengers Nottingham Forest in third place.
Di Matteo named an unchanged starting XI for the club's penultimate home game of the season, with fit-again Boro old boy James Morrison replacing Chris Wood on the bench.
Gordon Strachan made three changes as Gary O'Neil, Jonathan Grounds and Chris Killen came in for the injured David Wheater plus Jonathan Franks and Leroy Lita.
There was a real party atmosphere inside The Hawthorns as the fans turned up in their droves to celebrate automatic promotion, which had been sealed seven days earlier at Doncaster.
Although Albion had already achieved their season's target, Boro, who came down with the Baggies last season, had plenty to play for, having started the game seven points adrift of the final play-off berth.
The hosts responded to the crackling atmosphere and, inside two minutes, Brad Jones just beat Cox to a loose ball after Steven Reid had challenged for Graham Dorrans' free-kick.
The Teessiders recorded their first effort at goal in the fifth minute when Julio Arca volleyed well over from 20 yards.
The promotion party was in full swing in the stands - and it took less than eight minutes for the first Mexican wave to erupt!
Albion were displaying a real competitive edge and created the game's next opening on 19 when Robert Koren teed up Cox, who drew a fine save from Jones with an 18-yard rocket. Grounds' poor clearance fell to Chris Brunt who charged into the box before firing inches over from an acute angle.
Seconds later, Albion poured forward again but Grounds' last-ditch challenge took the sting out of Bednar's shot, providing Jones with an easy save.
Jones had much more trouble dealing with Brunt's ferocious shot from the edge of the box in the 25th minute when he spilled the ball, but the Boro No.1 pounced on the rebound before an Albion player could react.
Albion went agonisingly close to breaking the deadlock on 29 when the industrious Koren dispossessed Kyle Naughton and slipped in Bednar.
The Czech striker showed terrific footwork to jink past Naughton and Grounds before seeing his eight-yard shot from a tight angle cannon off the underside of the crossbar and fly to safety.
Albion continued to ask all the questions but Bednar headed harmlessly at Jones from close range after Boro had failed to clear Reid's long throw-in into the box.
Dorrans then went close when his low 25-yard shot evaded Jones' outstretched hand - before dribbling past the far post.
Boro did not threaten again until the 41st minute when Scott McDonald linked up well with former Celtic colleague Barry Robson before curling just wide from 15 yards.
But it was Albion who deservedly went in 1-0 up at the break - and in style.
In the second minute of stoppage time, Bednar chested Gabriel Tamas' ball into the path of Cox and the former Swindon striker skipped past Boro's central-defensive duo of Grounds and Steven McManus before planting an unstoppable 15-yard drive into the top right-hand corner.
Albion were forced into a change at half-time as Dean Kiely replaced Carson, who had needed lengthy treatment in the first half after a collision with McDonald.
The Baggies picked up from where they left off after the break and Jones had to be well-positioned to deal with Brunt's downward volley from Cox's cross.
Koren had an even better chance on 52 when the ball broke to him in the box after clever link-up play between Bednar and Cox, but the Slovenia skipper blasted wide of the near post.
However, Albion got the second goal their dominance deserved when Bednar made it two goals in as many games on 55.
The former Hearts man stabbed home from close range after Cox's header from Koren's cross had ricocheted off Grounds' back and fallen into the striker's path.
Albion weren't satisfied with the two goals as they continued to impress and Jones denied Cox's volley on the turn at point-blank range after Reid had headed Brunt's corner goalwards.
Dorrans tried to get in on the act but was well off target with a speculative 30-yard drive.
The Baggies went close again on 72 when Jones could only parry Koren's shot and the off-balance Bednar was unable to force home the rebound.
Two minutes later, Jones had to pull off a top draw save to deny Bednar, who been released by Koren.
Albion did not let up and, after Bednar flicked on Dorrans' cross, Jones just managed to claw the ball away from sub Morrison before he could pounce on Koren's header back across goal.
Jones was busy again when he had to frantically back-pedal to tip over Marek Cech's cross-cum-shot.
A minute later, Morrison curled just wide from 15 yards after being teed up by Reid from Dorrans' corner.
Boro regrouped briefly during the dying minutes and when Lita breezed past Tamas, the sub had the ball stolen off his feet by the alert Kiely.
A minute later, Boro defender Justin Hoyte saw a 25-yard volley dip over the bar.
In the first minute of stoppage time, the visitors came agonisingly close to bagging a consolation when McDonald headed Robson's free-kick off the left-hand post.
Albion almost made it 3-0 with virtually the last kick of the game when Morrison saw his goalbound strike deflected wide by McManus.
ALBION (4-5-1): Carson (Kiely HT); Reid, Tamas, Olsson, Cech; Koren, Cox (Morrison 75), Mulumbu, Dorrans, Brunt; Bednar (Miller 83). Subs not used: Barnes, Slory, Mattock, Meite.
MIDDLESBROUGH (4-4-2): Jones; Hoyte, Grounds (Riggott 71), Naughton, McManus; Williams (Franks 80), Robson, O'Neil, Arca; McDonald, Killen (Lita 54). Subs not used: Coyne (gk), Miller, Taylor, O'Shea.
GOALS: ALBION - Cox (45+2), Bednar (55).
BOOKINGS: MIDDLESBROUGH - O'Neil (foul 58), McManus (foul 66).
REFEREE: G Hegley (Hertfordshire).
ALBION STARMAN: Youssouf Mulumbu.