Millwall boss Neil Harris was left frustrated with his side’s organisation at a set piece as the Lions went on to throw away a two-goal lead in today's 3-3 draw with Derby.

The Rams scored a softly awarded free-kick from the edge of the area before the break as Thomas Ince curled the ball past a poorly contracted Lions wall, the strike creeping in at the near post.

Lee Gregory claimed his first hat-trick in professional football to put Harris’ side 3-1 up before a debatable penalty coverted my Chris Martin and an outstanding Jeff Hendrik volley saw the vistors restore parity.

But having seen his side 2-0 up on the cusp of half-time, Harris was left annoyed with his side's defending of the set-piece which gave Derby a way back into the game.

“It’s disappointing,” the manager said.

“To score three goals at home you'd expect to win the game. We've got enough senior players on the pitch and in the dressing room to see the game out.

“Their first goal was really poor. It was a poor set piece to concede from the free-kick and we didn't have the right set-up.

“The second one was a very soft penalty, I think the boy has done really well to buy it. It was a ridiculous decision.

“I think for their third goal, sometimes you have to hold your hands up and say 'what a great finish,' but to be 3-1 up is disappointing.

“I've not had a go at the players.

“If they get simple things wrong like the wrong shape on set-plays or our set-up isn't right, then words would be said.”

Aside from bemoaning his side's lack of set-piece cohesion, Harris could not hide his pride for Gregory after his first treble in the Football League.

The Den chief said: “He's scored two penalties today because he takes 10 a day in training now.

“That’s what he has to do to be a top player and score goals regularly. He has to practice everyday.

“Lee Gregory deserves those three goals, he’s an absolute top player.

“It'll give him real belief and next year for us, he will score 20 goals, whatever league we are in.”

Despite many fans conceding Millwall were certainties for relegation weeks ago, Harris feels his side have engineered a spirit through adversity in clawing their way back into survival contention.

“The players, as a group, have built hope and belief themselves,” Harris said.

“To come from being on the run they were on to come back and produce the performances and get some of the results that they've got has been testimony to the group of players.

“I’m certainly not accepting some well done’s for getting points at home, that’s the bottom line - you play for Millwall Football Club - you win your home games.”

Should Rotherham win their game in hand on Tuesday at home to Reading the Lions will have their relegation to League One confirmed ahead of next Saturday’s final league fixture.

Harris added: “While we've been behind them, it’s always been out of our hands.

“If we can't get more points than Rotherham, then they'd always finish above us - that doesn't change.

“It’s really simple. If Rotherham get a win on Tuesday, we get relegated.”