Josh Coburn returned to haunt old club Middlesbrough with a second-half double as Millwall came from behind to win their crucial Championship promotion encounter and go second in the table.

Boro dominated the first half and deservedly led through a header from captain Dael Fry.

But having been relieved to only go in one down, Alex Neil's side regrouped at half-time and responded when Coburn's powerful close-range volley squirmed through the grasp of goalkeeper Sol Brynn and crept over the line.

A £5m signing from Boro last summer, 23-year-old Coburn then delivered the decisive blow in the 86th minute when he steered a shot into the bottom corner.

The three points allowed Millwall to jump from fourth to second, leapfrogging Boro, who sink to third, with Ipswich Town, not in action on Friday, three points behind the Lions with two games in hand.

But defeat compounded Middlesbrough's jitters as it is now four games without a win for them after this painful loss.

Having gone top of the table in February on the back of six successive victories, Boro have only won two of the subsequent eight games.

The form of Kim Hellberg's side at home has been a particular concern, with the previous four matches producing only three points and just two goals, all against sides 16th or lower.

But they did not appear to have an issue as they made a rapid start, which should have produced a goal but Fry wasted a glorious chance, volleying over from six yards.

When Boro did hit the target, on-loan Sunderland goalkeeper Anthony Patterson saved well from Callum Brittain's drive from a tight angle.

But Fry made amends for his earlier miss when he headed home from four yards from Alan Browne's inviting cross.

He almost had a second but Femi Azeez was in the right place to clear his goalbound attempt as Boro could not deliver the dominance their play had merited on the scoreboard, with top scorer Morgan Whittaker and star midfielder Hayden Hackney still absent through injury.

Millwall have consistently been in the top six since early January, with strong form of 29 points from 14 games in that time.

That, allied with Boro's wobble, had allowed the automatic spots to loom into view, and they showed that with a strong 1-1 draw at Ipswich last time out confirming their credentials.

But, having been second best throughout the first half, the visitors came out of their shells after the break and Brynn had saved superbly from Tristan Crama's deflected effort before they did level.

Jake Cooper and Mihailo Ivanovic kept a corner alive and although Coburn's volley was straight at the goalkeeper, it was so powerful that it squirmed over the line.

To their credit, they did not settle for a point and Azeez and Zak Sturge had chances to put them ahead.

But the last word went to Coburn, as he produced a moment of ruthlessness in front of goal that Boro had lacked.

The home side lost possession in their own half and when substitute Barry Bannan found him in the left corner of the area, the boyhood Boro supporter took aim and placed a lovely low curling finish beyond Brynn's reach into the bottom corner.

Boro tried desperately to scramble a point in the five minutes of injury time, but Millwall held on as a return to the top flight for the first time in 36 years becomes a distinct possibility.

There is little time to digest this result as both sides are back in action again on Easter Monday.

Millwall host Norwich City at The Den (13:00 BST), while Middlesbrough make the long trip to south Wales to face Swansea City later that afternoon (17:15 BST).

Middlesbrough head coach Kim Hellberg told BBC Radio Tees:

"It hurts a lot. Sometimes it feels like some higher power up there tests us so much and we have to be strong.

"In many ways, I'm thinking this was a performance that should have killed the game off and been dead and buried after 60 minutes, 4-0 or 5-0.

"The boys were doing it unbelievably good after coming back one or two days ago against a good side, so it's tough."

Millwall manager Alex Neil told BBC Radio London:

"We were never coming to come here and pop Middlesbrough off the pitch. We're not that type of team.

"They're that type of team and I thought at times they were excellent at it. They're a really good side but what we are is even when we're not playing well, we stay in games.

"What we can do when we get our foot on the ball and show a little bit of composure is we can create opportunities and score goals because we've got guys at the top end of the pitch that can finish.

"And I thought today when the chances came along, we took them."