Jake Cooper’s header earned Millwall a point against the Championship leaders in a thriller at the Den.

Millwall had taken an early lead through Lee Gregory, but Diogo Jota and Romain Saiss struck on either side of half-time to put Wolves in front.

The visitors had chances to wrap up the three points, but Cooper nodded home with 18 minutes left to ensure a share of the spoils.

Here are five things we learned…

Gregory finally gets his goal

His performances have warranted more goals than his current tally shows, but that is partly down to his poor finishing. If work-rate alone counted for goals, he would be top of the charts.

Gregory missed two glorious chances against Derby County on Saturday, but was in no mood to let that happen against Wolves as he confidently slotted home after a fine pass from Jed Wallace to give Millwall the lead.

Gregory will be keen to add to his four goals this season when QPR travel to the Den on Friday, especially as he saw red against them earlier in the season when the sides drew 2-2 at Loftus Road.

Cooper on the scoresheet but could it have been more?

Neil Harris was keen to praise his 6ft 4ins centre-back for his late equaliser, but said that Cooper could have gone home with the match ball.

He climbed highest to nod home Millwall’s second, but missed two good openings in the first-half to add to that.

His second effort was his best chance, but he could only head into the side-netting when given a free header at the back-post.

Millwall continue to thrive in December

Despite the blip against Derby, Millwall’s impressive December continued against Wolves. It’s now eight points from five games.

Those five clubs currently occupy three of the six play-off places with the other two sitting in seventh and eighth.

The month began with wins at the Den against Sheffield United and Middlesbrough, either side of a hard-earned draw at Villa Park. They will hope they can finish the month in the perfect way with victory over QPR.

Another long-range effort beats Jordan Archer

For the third time in as many games, and the ninth time in total this season, Archer was beaten by a shot from outside the box.

It was a very similar goal to Stewart Downing’s for Middlesbrough as the goalkeeper got a hand to Jota’s 25-yard strike, but could only help it into the top corner.

Could 4-3-3 become a thing?

When Harris took Aiden O’Brien off eight minutes from time and replaced him with Ryan Tunnicliffe, you could have been forgiven for thinking he was settling for a draw and sticking with what he had by packing the midfield.

But it was clear to see within minutes that he was switching to a 4-3-3 formation, using Tunnicliffe in a midfield three with George Saville and Shaun Williams with Wallace pushing further forward on the left and Steve Morison pulling out to the right.

With Tunnicliffe’s impressive form in recent weeks and the return of Williams, could Harris consider a permanent change of formation?