Atletico Madrid took advantage of Carlo Ancelotti's decision to rotate as they edged out fierce rivals Real Madrid 1-0 on Sunday to tighten their grip on fourth place in LaLiga.
Four days on from their stunning comeback win over Manchester City in the Champions League semi-finals, Madrid made seven changes for their trip to Wanda Metropolitano.
That told as Madrid, who were crowned Spanish champions last week with four games to spare, fell behind to a 40th-minute Yannick Carrasco penalty that was awarded after a VAR check.
Despite the introduction of Luka Modric and Vinicius Junior, Madrid could not find a leveller in the absence of top scorer Karim Benzema as they fell to a rare El Derbi defeat.
Much was made of Atleti's decision to not give Madrid a guard of honour ahead of kick-off in their neighbours' first league outing since sealing a 35th league crown.
The home side were far more fired up for the match and twice went close in the opening eight minutes, with Angel Correa and Carrasco firing wide from good positions.
Carrasco made the breakthrough from the penalty spot before half-time, though, after Matheus Cunha was barged over by Jesus Vallejo just inside the box.
The referee had initially allowed play to continue for a couple of minutes, but he was instructed by the VAR to check the pitchside monitor and reversed his initial decision.
Luka Jovic was denied by Jan Oblak and Casemiro should have done far more with a tame shot that was curled straight at the Atletico keeper as Madrid pushed for a leveller.
Atleti wasted chances of their own as Carrasco fired over and Cunha could not convert past Andriy Lunin when played in by substitute Antoine Griezmann, who also went close.
Carrasco nearly sealed things when hitting the post 14 minutes from time, but his earlier penalty proved enough in the end thanks to another Oblak save to keep out Vinicius and a bad miss from Nacho.
The derby is ours! pic.twitter.com/9HndUO8mjg— Atlético de Madrid (@atletienglish) May 8, 2022
What does it mean? Rare derby delight for Diego's men
Having wrapped up the league title with time to spare, Real Madrid can afford to rest up their key men ahead of the Champions League final against Liverpool on May 28.
Ancelotti did exactly that against Atletico and it told as his side were far from their best, with this their first league loss against Los Rojiblancos in 12 matches.
Diego Simeone's side are now one point behind third-placed Sevilla, though more importantly they have a six-point advantage on Real Betis in fifth.
Carrasco keeps his cool
The big moment in the match was undoubtedly the penalty awarded to Atletico shortly before half-time, which Carrasco calmly converted by sending Lunin the wrong way.
That was the first penalty Atleti have scored against Madrid in LaLiga since March 2010, when Diego Forlan held his nerve from 12 yards.
Madrid miss main man Benzema
Benzema has been directly involved in 57 goals for Madrid in all competitions this season, with no player in Europe's top five leagues able to match that incredible tally.
With the striker spending the full 90 minutes on the bench here, Los Blancos' profligacy told as they failed to find the net from any of their 15 shots, six of which were on target.
Atletico travel to Elche for their next LaLiga outing on Wednesday, while Madrid host relegation-threatened Levante the following day.