A last-gasp penalty from Gonzalo Higuain gave Real Madrid a late, late 2-1 win away to luckless neighbours Atletico on Saturday.
Real were given the penalty five minutes into injury time after a clumsy foul by John Heitinga on fellow Dutchman Royston Drenthe, reports dpa.
Simao Sabrosa seemed to have given Atletico a point by making it 1-1 with a handsome free-kick in the 90th minute.
But, as usual, Real never stopped looking for victory - and scored another of their trademark injury-time wins.
"We didn't win to draw tonight," said a delighted Higuain, "and I think we just about deserved the three points."
The whites are now top of La Liga, albeit temporarily, on goal difference over Valencia and Villarreal, all three teams now on 16 points.
Villarreal will go top if they manage to avoid defeat away to midtable Espanyol later on Saturday. Valencia are at home to lowly Numancia on Sunday.
Atletico have not won a Madrid derby since 1999, and never looked like doing so this time after making a nervous start and conceding a goal in the very first minute.
Van Nistelrooy took a pass from Marcelo out on the left, held off fellow Dutchman John Heitinga - and scored with a low far-post drive.
In the 22nd minute Van Nistelrooy appeared to have made it 2-0 but was wrongly ruled offside.
It was the first of many mistakes by disastrous referee Clos Gomez.
In the 31st minute he harshly sent off Atletico defender Perea for elbowing Wesley Sneijder, then nine minutes later gave Van Nistelrooy an absurd red card for allegedly diving.
Goalkeeper Leo Franco kept Atletico in the game in the first half, but counterpart Iker Casillas was the more active of the keepers after the interval.
Simao made it 1-1 with his classy free-kick in the 90th minute, and the hosts seemed to have salvaged a draw. But five minutes into stoppage time super-sub Drenthe broke free and was pulled down by Heitinga - giving Higuain the chance to win the game from the penalty spot.