Late goal specialists Millwall had the tables turned on them as Middlesbrough striker Leroy Lita headed an 83rd-minute winner to settle an action-packed five-goal thriller at The Den.
In a topsy-turvy encounter The Lions edged into a 1-0 lead courtesy of Neil Harris' 15th-minute strike, only for Boro to level score twice in four second-half minutes through Tony McMahon (58mins) and Scott McDonald (62mins).
Debutant Hameur Bouazza struck a stunning free-kick to level the scores at 2-2 on 78 minutes only for Lita to steal in and glance Merouane Zemmama's tantalising cross beyond the reach of Lions keeper David Forde.
"Middlesbrough are a good side," said boss Jackett. "They moved the ball very well, although the first goal was a very soft one to give away.
We were disappointing defensively, but our spirit throughout the game was excellent. Overall, it was a great game but that's no consolation for me, we dominated at times but really needed that second goal when we were ahead."
That The Lions finished empty-handed on the points front merely added to the sense of frustration as Kenny Jackett's side dominated large spells of the game, a fact indicated by a corner count of 18 for the home side to Boro's two.
A pulsating match saw The Lions force their first corner after 19 seconds and three minutes to come within a whisker of opening their account.
Great work by Chris Hackett set Scott Barron racing into space, he picked out James Henry and although the latter's cross was hacked clear, the ball fell invitingly for Steve Morison who instinctively stuck out a boot, the ball flashing agonisingly wide of Jason Steel's left-hand post.
At the other end the lively Lita wasted two golden opportunities in as many minutes, failing to find the target with either. First he directed a header from McMahon's deep cross over the bar on six minutes and then seconds later producing a heavy first touch that took the ball out of play as he attempted to round keeper Forde.
It took a fantastically timed tackle by skipper Paul Robinson to avert the danger on eight minutes with James Henry's stunning effort smacking the top of the cross bar in a breathtaking opening 10 minutes.
Something had to give, and on 15 minutes it was the Boro defence. Forde launched a long clearance downfield, Morison won the flick on, and Neil Harris stole behind the Boro defence to volley past Steele from close range - his first goal in the Championship this season.
Striker partner Morison came close to adding a second with a half-volley that sailed over the crossbar shortly after the half-hour mark and Henry twice lashed narrowly off target from distance as The Lions pushed forward in search of a second goal.
Millwall had the first of two penalty appeals waved away when Morison's snap-shot looked to be palmed away by a stray Boro hand and the ball flew behind for a corner.
Boro were by no means spectators in an absorbing opening half and it was Lita who wasted yet another glaring opportunity for the visitors. Julio Arca released the former Reading forward, but the imposing figure of Forde forced Lita wide enough to enable the backtracking Robinson to get back and mafe another crucial clearance from his own goalmouth.
The second half started in the same vein as the first with Millwall forcing two corners and Morison directing a header from Barron's teasing delivery just wide of the mark.
But from nowhere, McMahon fashioned a sensational equaliser for the visitors in the 58th minute.
Darren Purse was penalised for a foul on McDonald and McMahon did the rest with a superb curling 25-yard effort that left Forde grasping at thin air.
If the equaliser had come out of the blue, Boro's second four minutes later stunned the home fans. Substitute Merouane Zemmama, who had entered the fray seconds before McMahon's leveller, was the instigator, twisting past two defenders on the edge of the area and whipping over a super cross to McDonald, who in turn drilled a low finish past Forde.
Lions boss Jackett introduced debutant Bouazza for his first action in a Millwall shirt, and with 12 minutes remaining he drilled a fantastic strike into the top left-hand corner to haul The Lions level at 2-2.
But back came Boro again though, and the visitors reclaimed their lead with seven minutes left.
Zemmama was again involved, picking the ball up on the right-hand side and delivering a teasing cross into the box for Lita, who stole ahead of his marker to glance home from eight yards.
Millwall threw caution to the wind thereafter and pushed on again in a desperate bid to claw their way back once again.
Liam Trotter had a snap-shot smartly stopped by keeper Steele and sub Kevin Lisbie was sent sprawling by Seb Hines as he prepared to pull the trigger, only for referee Chris Sarginson to wave away appeals for a spot-kick to the disbelief of the home fans and relief of a Boro side that clung on through six additional minutes of stoppage time for three priceless points.
Millwall: Forde, Dunne, Barron, Abdou, Robinson, Purse, Hackett (Bouazza, 64mins), Trotter, Harris (Lisbie, 75mins), Morison, Henry. Subs not used: Mildenhall, Eastmond, Craig, Ward, T.Robinson.
Bookings: Henry (62mins), Morison (80mins)
Scorers: Harris (15mins), Bouazza (78mins)
Middlesbrough: Steele, Bailey, McMahon, McDonald (Smallwood, 90+2mins), Hines, Arca (Zemmama, 56mins), Lita, Bennett, Taylor, Grounds, Davies. Subs not used: Ripley, Park, Halliday, Boyd, Haas.
Bookings: Arca (54mins), Davies (76mins), Lita (83mins)
Scorers: McMahon (58mins), McDonald (62mins), Lita (83mins)
Ref: C. Sarginson
Att: 11,871 (away 878)