Jordan Hugill's 90th-minute penalty-kick gave Middlesbrough a share of the spoils at the Riverside Stadium on Saturday afternoon as Millwall drew 1-1 in the Sky Bet Championship.
Jed Wallace gave the impressive Lions a 22nd-minute lead, but Hugill converted a spot-kick as the clock struck 90 minutes to deny Millwall a second successive away victory.
Neil Harris made five changes from last Saturday's 2-0 defeat at home to Blackburn Rovers, facilitating a change of formation, as Murray Wallace, Shaun Williams, Ben Thompson - for his first Sky Bet Championship start - Lee Gregory and Ben Marshall - for his second Lions debut - replaced James Meredith, Ryan Tunnicliffe, Aiden O'Brien, Tom Elliott and Shane Ferguson.
The Lions had a spell of attacking play inside the first three minutes, but despite numerous crosses into the box, they were unable to find a way past a resolute Middlesbrough defence.
On 10 minutes, with Millwall's dominance continuing, a Shaun Williams corner-kick lead to Gregory having a stab at goal from close range, but his effort was well stopped by Darren Randolph. A run from Jed Wallace then set up the striker from an acute angle, but he found the side-netting.
With 22 minutes on the clock, The Lions took a deserved lead through Jed Wallace. Gregory robbed Adam Clayton of possession just inside the Millwall half and ran towards goal, before setting up the winger to slot past Randolph from inside the penalty area.
Lewis Wing had Boro's first attempt of the afternoon just a minute later, but he shot wide, before Millwall piled on more pressure, ending with Thompson heading into the arms of Randolph. Clayton's cross was then headed wide by George Saville as the first-half reached its last 10 minutes.
On 38 minutes, Jordan Archer had to be at his best to stop Middlesbrough's most promising chance of the game, tipping wide as Jonny Howson looked to nod Clayton's cross towards goal.
Half-time substitute Rajiv van La Parra was causing The Lions' defence problems as the second-half got underway, and his pace and trickery began a succession of set-pieces for the home side around the 50-minute mark, but Millwall dealt with them comfortably as they came to an end with Daniel Ayala heading wide.
Wing forced Archer into palming away a stinging effort on 57 minutes, before Howson blasted just over as Boro began to turn the screw. Saville opted to shoot instead of feeding the unmarked Howson a minute later, with Jordan Hugill slicing over on the hour-mark.
Jed Wallace stole the ball away from the Middlesbrough defence on 68 minutes, but with Randolph rushing out of his goal, the stopper reached the ball first.
The introduction of Steve Morison with 10 minutes remaining allowed Millwall to keep the ball and take the sting out of the Middlesbrough wave, and they fashioned a chance with five minutes to go, but Mahlon Romeo flashed an effort wide.
Thompson's fantastic cross-field pass found goalscorer Jed Wallace with 87 minutes on the clock, but his attempt went just wide of the post.
However, The Lions' hard work was undone in the 90th minute as referee Keith Stroud awarded a penalty-kick after Morison pushed Ayala inside the six-yard box - Hugill stepped up and sent Archer the wrong way.
Middlesbrough: Randolph, Friend, Ayala, Batth, Clayton (van La Parra 46'), Hugill, Howson (Assombalonga 61'), Fry, Saville, Wing, Besic (Downing 69'). Subs not used: Dimi, McNair, Fletcher, Flint.
Scorer: Hugill pen 90'
Millwall: Archer, Hutchinson, Cooper, Williams, J. Wallace (O'Brien 88'), Thompson, Gregory (Morison 80'), Romeo, M. Wallace, Leonard, Marshall (Ferguson 72'). Subs not used: Martin, Onyedinma, Pearce, Tunnicliffe.
Scorer: J. Wallace 22'
Referee: Keith Stroud