Jason Puncheon marked a dream debut with a 25th-minute winner as Millwall sent Middlesbrough plummeting into The Championship drop zone with victory on their first ever visit to the Riverside Stadium.
It was 43 long years ago when The Lions last tasted success against Boro away from The Den, new or old, but Puncheon - one of two debutants in The Lions team - ensured that the 863 strong band of travelling fans enjoyed a happy trek back down south, sweeping home Liam Trotter's cross to clinch a thoroughly deserved maximum point haul.
Lions keeper David Forde may have come to the rescue twice in the first-half with superb athletic saves, but it would have been a travesty of justice if Tony Mowbray's men had taken anything from this game.
"What a terrific result. I'm very pleased," enthused Jacket.
"It was a sterling team performance and obviously it's nice for Jason Puncheon to score the winning goal on his debut.
Although it was a fantastic win, we still need to find more goals and had a number of chances to make the win more comfortable.
I must thank the fans who came up here though; once again they really helped the team with their support and it's pleasing that we have paid them back by getting a very good result."
Jackett made three changes to his starting line-up in a bid to find a winning formula with debutants Calvin Andrew and Puncheon replacing John Marquis and the injured Danny Schofield respectively.
Tony Craig returning for only his sixth league start of the campaign completed the trio of players drafted in, slotting in at left-back for Scott Barron, who missed out through suspension.
Millwall's last visit to Middlesbrough came in 1994 when The Lions returned home with their tails firmly between their legs on the back of a 3-0 defeat.
But having never visited Boro's Riverside Stadium before, the slate was effectively clean. A fresh start it was indeed in more than one way as The Lions played with renewed vigour and verve, in the process reproducing the kind of solid, professional display that served them so well during last year's promotion-winning campaign.
Two corners in the first 58 seconds gave an early indication that Jackett's men were going to try and impose themselves on proceedings from the start, and that's exactly what they managed to do in a first-half that was by and large dominated by the visitors.
Steve Morison was a whisker away from connecting with James Henry's delivery after ghosting in unmarked at the far post on four minutes, but home keeper Jason Steele intercepted with a smart catch.
Then on six minutes a long goal-kick from David Forde was headed on by Liam Trotter to Puncheon, and he drove forward before hitting a left-foot effort straight into the keeper's hands as The Lions pressed.
At the other end Boro had a brief flurry of attacking pressure during which David Forde did brilliantly to deny Gary O'Neil, somehow arching backwards enough to tip his looping deflected shot over for a corner.
Forde then comfortably dealt with Barry Robson's smart shot on the turn from 20 yards as the home side began to ask questions of The Lions rearguard.
But Boro's spell of pressure didn't last long and instead it was Millwall who looked the sharper and more inventive side.
Morison twice went close, lashing over from 10 yards and then picking up Andrew's flick from a Forde clearance and firing narrowly over.
Something had to give and The Lions didn't have to wait much longer for the goal their approach work deserved on 25 minutes.
Henry intelligently slipped the ball down the line to Trotter, he in turn spotted Puncheon's powerful run into the danger zone, squared the ball to the Southampton lonee and Puncheon did the rest, sweeping home from 12 yards in fine style.
It was so nearly 2-0 when the impressive Puncheon saw his sweetly struck free-kick flash inches wide of Steele's left-hand post with the keeper rooted to the spot.
Forde, who was a spectator for long spells of the game, was called into action when he backpeddled to somehow get his fingers to claw away Luke Williams' looping goalbound header just before the break, but it was The Lions who went in with a valuable goal in the bag.
Not surprisingly Boro came flying out of the traps at the start of the second-half and it was only a split-second piece of hesitation by Leroy Lita that prevented the striker having a clear shot at goal from six yards.
Morison then saw his effort deflected for a corner after Henry's perfectly weighted pass had sent him racing through at the other end as the teams traded early scoring chances.
Puncheon slammed the ball into the side netting after 56 minutes following another quick Lions break and Boro boss Tony Mowbray responded by making a double substitution, introducing Marvin Emnes and Mickael Tavares for the ineffective Kris Boyd and Julio Arca.
If Mowbray had been hoping for an instant response he was left bitterly disappointed as Boro huffed and puffed but on too many occasions were devoid of a penetrative final pass.
It took until 78 minutes for the home side to muster another attempt on goal when defender David Wheater tried his luck from 25 yards out. That he hopelessly skied a shot which cleared the roof of the stand, sailed out of the ground and is probably still travelling was some indication of how ineffective Boro were in the final third.
It was ironically only when the fourth official showed six minutes of injury-time that the home side sprung into life.
Lita sent a bullet header from Williams' cross agonisingly wide in the first of what proved to be seven minutes of time added on.
Although the majority of the minutes were ultimately played out in front of the Lions fans by the corner flag as Morison won a sucession of throw-ins and corners by consistently banging the ball against whoever was in a red shirt in front of him, it took a last-ditch clearance off the line by winger Henry to prevent Wheater's 96th-minute effort stealing in at the near post.
That it was Henry, who worked his socks off and produced one of his best all-round displays in a Millwall shirt, summed up the real essence of an excellent team performance.
Middlesbrough: Steele, Bates, Wheater, Boyd (Emnes, 59mins), Lita, Robson, O'Neil (Bailey, 41mins), Arca (Tavares, 59mins), Williams, Bennett, McMahon. Subs not used: Ripley, Hoyte, McDonald, Kink.
Booking: Bennett (32mins)
Millwall: Forde, Dunne, Craig, Trotter, Robinson, Shittu, Puncheon, Mkandawire, Morison, Andrew (Harris, 85mins), Henry. Subs not used: Mildenhall, Carter, Ward, Laird, Abdou, Marquis.
Scorer: Puncheon (25mins)
Ref: T. Kettle
Att: 15,697 (away 863)