Diego Costa says that he never takes his work home with him. Which is probably a good thing. If he did, the Atlético Madrid striker might walk through the door, goad the dog with a stick, surreptitiously elbow his wife out of the way on the stairs, shrug his shoulders innocently as she lay in a crumpled heap at the bottom and whisper insults to his children, look the other way and whistle when they burst into tears. He might stroll into the living room and dramatically collapse on the floor, roll around the rug holding his head and appeal for a penalty. He might even get it too.

Yes, Costa is one of La Liga's finest wind-up merchants. Plenty of people don't much like what he does yet they can't help but admit that he's very good at it. If other teams' fans hate him, his fans love him – a little guiltily, perhaps, but still – and even those who hate him sometimes can't help a sneaky smile. There is, after all, something a bit comic about it, something a bit cartoon bad guy. His is a dangerous game but it can be a pretty successful one too. And Sunday night summed it up perfectly. "Dr Jekyll and Mr Costa" Marca's headline called him.

They'd been waiting for him, cosh in hand – and on Sunday night Real Betis took revenge. Nasty, vicious, dirty revenge. On Sunday night Costa was not the bad boy; they were. He was the victim. But no one seemed to feel sorry for him and, when the final whistle went, he was also the victor. It's Costa on the cover of the newspaper, arms out celebrating, a huge grin on his face. When the final whistle went on the weekend's final game he grabbed hold of the ball and booted it into orbit, shouting in delight. In Monday morning's papers he claims one of AS's weekend awards. Gold for Lucas Alcaraz, the debutant Granada coach who defeated Real Madrid; Frankincense for Víctor Valdés, who rescued Barcelona against Valencia and Myrrh for Costa. Whatever Myrrh actually is.

The reason was simple: his goal had given Atlético Madrid a 1-0 win, securing their 20th consecutive victory at the Vicente Calderón and his entrance had changed the game. It had seen Atlético close the gap on Barcelona and open the gap on Real Madrid, leaving them wondering if challenging for the title is not so impossible after all. "I'm pleased about the victory," Costa said. As for all that other stuff, he wasn't budging. Three times they asked him. Three, four, five times, in fact. And he just smiled. "What happens on the pitch, stays on the pitch," he said.

What happened on the pitch was not much really. Not until he came on after an hour. It was Atlético Madrid versus Real Betis and it was 0-0. It was not going to stay that way for long. A storm broke. It was about to become a different game entirely, whichever way you looked at it. As one match reporter put it: "Suddenly, the piped music of chiropodists' waiting room became a heavy metal gig." El País called him "The Revolutionary". And El Mundo insisted: "Diego Costa came on and the Calderón quaked … Atlético Madrid quaked and Betis quaked. The referee quaked, and so did Diego Simeone and Pep Mel and the presidents and the kit men and the ball boys. The fans quaked and the M30 motorway that passes by and the trees and even the Puerta de Toledo."

It took less than five minutes for Costa to score the opening goal and not very much longer to plant a full set of studs on Rubén Pérez's shin. It was a miracle he didn't do any damage. Things were heating up.

They had been heating up for a while. The last time these two teams faced each other was just over a week ago in the Copa del Rey. The Betis centre-back Antonio Amaya gifted Costa the goal, heading past his own goalkeeper and leaving the Brazilian with an open goal. When they got down into the tunnel Costa rubbed it in. "He was very grateful," Amaya said afterwards. "He was shouting and thanking me for the gift. If my team-mates had not held me back, I would have killed him. That shows what kind of person he is: he has no heart and no shame."

Now Amaya and his team-mates were waiting to give him a taste of his own medicine. Live by the sword, die by the sword. "You knew that they would go for him ever since [the game in] Seville," the Atlético centre-back Diego Godín said. The challenge on Pérez only made that even more certain. "Costa is a difficult player to put up with," said Perquis. Betis did not.

And so it started. Costa challenged José Cañas. There was not much wrong with it but he spun and twisted and crashed into a dramatic heap. As the ball ran loose Pérez walloped Cebolla. In they piled, pushing and shoving. Thirteen players came together. Costa was not one of them. He soon would be. Next time Atlético were in the Betis penalty area, the moment had come. Amaya approached Costa, leaning in. Blink and you'd miss it but next thing you knew, Costa was spinning round and there was the evidence: a great big globule of gob on the side of his face.

Somehow, spitting always seems the ultimate of sins; a face full of gob is worse than a face full of blood. To judge by the reaction, this was worse than if Amaya had just punched him: sneakier, dirtier, more disgusting. Even though spitting is far less likely to do damage than punching. As for Costa's insistence that what happens on the pitch stays on the pitch, there's something questionable, and probably self-interested, about that too: why should cheating necessarily be forgotten the moment the whistle goes, or the tunnel treated as a state without law? Why should there be a 90-minute statute of limitations? Football as love and war – a territory where all is fair. But all is not fair, not even in love and war.

That though is the code to which Costa adheres. And there was something about the fact that he applies it to himself too. As the final whistle went Costa had to be held back. He grabbed the ball and hoofed it into the sky, then headed down the tunnel, where he tore off his gloves and threw them to the ground, still fuming. But by the time he appeared under the north stand and faced the media, he was happy. As if he accepted that the way he plays brings with it risks and he is prepared to take them, even if it means getting kicked to bits. As if getting gobbed on is just an occupational hazard. One scenario he had already encountered against Madrid, incidentally, and one he took, almost literally, on the chin. "They kicked Diego a lot and he behaved," said Mario Suárez.

"There are no scores to settle and no problems," Costa said afterwards. "What goes on the pitch stays on it. I don't take it home with me." Not least because what he did take home were three more points. His goal had given Atlético another win: 20 in a row at the Vicente Calderón, 12 out of 12 in the league and just six goals conceded – three of them in a single game. They are seven points clear of Real Madrid, 15 clear of Betis, the last of the non-Champions League teams, and just nine points off Barcelona. "People are talking about Madrid but our rivals are Atlético Madrid," said Dani Alves.

Talking points

• Real Madrid appear to be a normal football team but every time they venture south something funny happens. For every time it happens they are transformed into … a really, really bad team. This weekend they travelled to Andalucía for the fourth time this season. And for the fourth time this season they were defeated. Sevilla, Betis, Málaga and now Granada. Madrid created pretty much nothing; Granada created literally nothing. But still won, thanks to a Cristiano Ronaldo own goal – "Granada's" only shot on target all game. They are now 16 points behind Barcelona and have definitively given up on the league title.

• Incidentally, back when José Mourinho was Chelsea manager one of his favourite weapons to use against Rafa Benítez was to declare it easy to compete for the Champions League when you don't have to compete for the league … will his theory be proven right this season in Spain?

• Rayo lost 2-1 to Sevilla, fast improving under Unai Emery. Sevilla's goals were scored by Coke and Alvaro Negredo, who have one thing in common … they're Rayo youth team products.

• If Diego Costa doesn't take his football problems home with him, Ever Banega does not take his personal problems on to the pitch with him. At 10am on Thursday morning Banega was supposed to be in training. Instead, he was in bed. When the call came it woke him up. He leapt out of bed and dashed to Paterna, arriving just three minutes before the session was due to start and, according to some reports, "in a bad condition". It's not the first time either. This is the midfielder that did a spot of one handed web-chatting, got done for running a red light over the limit, saw his car burst into flames and broke his ankle when he was run over by his own car having left the handbrake off. The thing is, he can actually play a bit. Ernesto Valverde, who denied that he was in "bad condition", put him in the side against Barcelona and he scored the opening goal in a 1-1 draw. Valencia probably deserved more, too: Víctor Valdés made a great save in the last minute. As for Leo Messi, he scored for a 12th consecutive game, a La Liga record, thanks to a rocket of a penalty, but both he and Barcelona looked tired.

• Xavi and Xabi both miss Spain duty this week with injuries. See if you can guess which one is "injured" and which one "didn't fancy it", according to El Mundo Deportivo.

• Spain's winter transfer window: the frightening reality, laid bare. Less money was spent in the whole of Spain than QPR spent on Chris Samba alone; less money was spent in Spain than in Belgium or Turkey. And even the silver lining has a cloud. Roberto Soldado, Fernando Llorente and Negredo are all still here. Come next season, they probably won't be. Llorente will be at Juventus; six months of limbo await. Athletic have lost a player and not even succeeded in getting any money for him.

• Blimey. Espanyol do it again. They're now five points clear of the relegation zone, having lost only once since Javier Aguirre took over.

Results: Valladolid 2-2 Athletic, Osasuna 1-0 Celta, Getafe 3-1 Deportivo, Espanyol 3-2 Levante, Granada 1-0 Real Madrid, Málaga 1-1 Zaragoza, Sevilla 2-1 Rayo, Valencia 1-1 Barcelona, Atlético 1-0 Betis, Real Sociedad 2 - 0 Mallorca.

• Latest La Liga standings