And then there was one.
First-half goals from Alvaro Cejudo, Emiliano Armenteros and Roberto Torres rocked Diego Simeone’s side, who mustered little when asked to make a comeback.
It was Atletico’s second straight defeat away from home in La Liga.
The repercussions will be felt in Spain. Here are the takeaways from a night to forget for Los Rojiblancos.
If this weekend’s Spanish football had been scripted, Carlo Ancelotti would almost certainly be the man who directed it.
After his Real Madrid side beat a determined Elche side on Saturday afternoon, he’d have watched with half a smile as Barcelona unraveled in San Sebastian against Real Sociedad later that night.
Simeone might have been smiling too, but he wasn't smiling by Sunday night.
Atletico Madrid’s defeat in Pamplona leaves them three points off Madrid, level with Barcelona in second place in La Liga.
It’s been fun having a three-way tie at the top, but you get the feeling Los Blancos may be a bit more ruthless now that they’ve been granted some breathing space of their own—it’s been quite the year for Ancelotti so far.
Not that it will mean much to weeping Atletico fans on Sunday night, but El Sadar is proving a tough place for anyone to go—especially for Spain’s top three.
Barcelona plundered to a 0-0 draw there earlier in the season, while Real Madrid had to come from 2-0 down to snatch a late point when they travelled north to take on Osasuna in the league.
Unfortunately for Atletico, their experience there was slightly more painful.
The three first-half goals had all but killed the match by half-time, and "El Cholo" will now have to show his man-management skills as he attempts to pick his team up for the visit of Madrid to the Vicente Calderon next weekend.
It’s easy to seek problems when things aren't going well, but it does seem Simoene has got the rotation game worryingly wrong.
When Atletico Madrid were flying at the start of the season, they largely stuck with the same side week in, week out. However, it seems what benefitted them then is coming back to bite them now.
Recent rotations haven’t proved effective, and they have lost their last two matches on the road against Almeria and, now, Osasuna.
Hindsight makes it easier, but it's tempting to ask if El Cholo could have been a little more forthcoming with his changes when things were going so well earlier in the campaign.
Just one here or one there.
It might be purely coincidence, but Diego Ribas’ triumphant return to the Spanish capital is on the verge of spiraling into a calamity.
His starts since his return have come in two defeats against Real Madrid, the reverse in Almeria and the latest setback, on Sunday night, in Pamplona against a resilient Osasuna outfit.
Diego was found trying a few too many killer passes at El Sadar and, perhaps, it’s something to do with him not having had time to adapt to Atletico’s rigid structure and tactics.
At a team built on strength and consistency, Diego’s second spell is not yet proving all that it was hoped it would be.
The only good thing to come from Atletico’s defeat to Osasuna, if you can call it that, is that three of their main men managed to avoid the yellow card which would have kept them out of next weekend’s Madrid derby.
Diego Costa, who was suspended for the second leg of the Copa del Rey semi-final, was one of the three men on the verge of a suspension.
You can bet he’ll pick up the necessary yellow card in next week’s top-of-the-table clash.
Defenders Diego Godin and Filipe Luis were the other two men who managed to dodge the booking that would have confused Los Rojiblancos’ preparations for what is looking like a season-defining game.