Match ends, Middlesbrough 2, Derby County 0.
Middlesbrough scored twice in the final 10 minutes to win the battle of the top two against Derby and stretch their Championship lead to four points.
Boro, who have now set a club record of nine home league games without conceding, dominated early on, forcing Lee Grant to make two fine saves.
But just as the Rams seemed set to earn a point, Albert Adomah raced through to chip the opener after 82 minutes.
And within two minutes David Nugent teed up George Friend for the second.
Boro needed just a draw to stay at the top of table but, despite looking intent on stretching their one-point lead following a bright start, Derby looked to have done enough to secure a draw after an uninspiring second half.
The hosts, who are now unbeaten in eight league games, committed men forward from the off and quickly seized control of the midfield as the Rams sat deep.
Boro dominated possession and created numerous chances, with Cristhian Stuani and Emilio Nsue both heading decent chances off target, Adomah shooting wide and Rams keeper Grant making a couple of impressive saves - most notably a brilliant fingertip effort to keep out Friend's strike.
The visitors settled and, although they created very little, the pace and direct running of Johnny Russell provided a constant threat.
He should have done better with a close-range chance before the interval and Chris Martin also headed narrowly wide.
But Boro got back on top in the second half and they upped the tempo in the closing stages to secure victory.
Adomah's clever run and cool finish from Grant Leadbitter's pass put them ahead.
And substitute Nugent then unselfishly laid on a simple close-range second for Friend to earn a fourth consecutive win and end Derby's eight-match unbeaten run.
Middlesbrough manger Aitor Karanka:
"It was an amazing game, it's important for us to win. We're the best team now because we're top, but it doesn't mean anything in January with another 22 games to go.
"We're in a really good condition and we have to keep going. One month ago Hull were five points above us and now we're five points above them, but at this stage we've done nothing and there's a long way to go.
"The emotions are difficult to explain because there was a lot of pressure on us. We're proud of the defensive records we're setting. It's proving hard to create chances against us."
Derby head coach Paul Clement:
"Middlesbrough played very well with good intensity but we weren't at that level for the start, only in spells.
"We edged it on chances in the first half but with 20 minutes to go I made, you could argue, a quite bold change with an attempt to create a good chance and it didn't work. Soon after that they scored and they scored again and it's game over. I have to take full responsibility for that.
"We didn't play as well as we can but Middlesbrough deserved to win. I'm holding my hands up for making an attacking change."
- 9KikeSubstituted forNugentat 59'minutes
- 18ButterfieldSubstituted forWeimannat 76'minutes
- 34ThorneSubstituted forHendrickat 23'minutes
- 15JohnsonBooked at 77mins
- 9MartinBooked at 12mins
- Neil Swarbrick
- Shots on Target
Second Half ends, Middlesbrough 2, Derby County 0.
Attempt blocked. Tom Ince (Derby County) left footed shot from long range on the right is blocked.
Johnny Russell (Derby County) wins a free kick in the attacking half.
Foul by Albert Adomah (Middlesbrough).
Attempt missed. Johnny Russell (Derby County) left footed shot from the centre of the box is high and wide to the left. Assisted by Tom Ince.
Cyrus Christie (Derby County) wins a free kick in the defensive half.
Foul by Albert Adomah (Middlesbrough).
Goal! Middlesbrough 2, Derby County 0. George Friend (Middlesbrough) left footed shot from very close range to the centre of the goal. Assisted by David Nugent.
Attempt blocked. Cristhian Stuani (Middlesbrough) right footed shot from outside the box is blocked. Assisted by Grant Leadbitter.
Goal! Middlesbrough 1, Derby County 0. Albert Adomah (Middlesbrough) right footed shot from the right side of the box to the high centre of the goal. Assisted by Grant Leadbitter with a through ball.
Attempt blocked. Stewart Downing (Middlesbrough) left footed shot from outside the box is blocked. Assisted by Albert Adomah.
Attempt missed. Jason Shackell (Derby County) header from the centre of the box is too high. Assisted by Tom Ince with a cross following a corner.
Corner, Derby County. Conceded by George Friend.
Tom Ince (Derby County) wins a free kick on the right wing.
Foul by Ben Gibson (Middlesbrough).
Bradley Johnson (Derby County) is shown the yellow card for a bad foul.
Foul by Bradley Johnson (Derby County).
Cristhian Stuani (Middlesbrough) wins a free kick in the attacking half.
Substitution, Derby County. Andreas Weimann replaces Jacob Butterfield.