Diego Costa hit the post against Getafe. Painfully so. There were six minutes remaining and it was 1-0 to Atlético Madrid when Adrián laid the ball across the face of goal from the right; it was escaping the striker but he was not going to let it go, so he flew at it, launching himself. The ball hit the back of the net and Costa hit the post. Hard. The goal secured a vital victory that kept Atlético top of the table, but Costa was down. The full-back Filipe Luís approached him and immediately signalled to the bench. As he turned away he looked to the sky and mouthed: "madre mía".

Below the knee, Costa's shin had split open revealing the bone below. He did not want to look, drawing his hands over his face as he was carried off on a stretcher, motionless. In the stands, they feared the worse. As Costa went down the tunnel some worried that he might be taking Atlético's title hopes with him; success against Barcelona without him had not disguised how important he is. The first question asked of Diego Simeone was about him. "He's fine," said the manager, relieved.

The post was a different matter.

"Another scratch doesn't hurt a tiger," Simone said, smiling. There was something about it that summed up Costa and Atlético: the determination, the fight and the sacrifice, so competitive it hurts. He was, Simeone said, the image of the side; a side that leads the Spanish league with four games to go and faces Chelsea in the semi-finals of the Champions League.

This season, Costa became the Champions League's best debutant with seven goals in his first six games. His goal against Getafe was his 26th in the league; on Friday night another one made it 27. That has not been thanks to the occasional hot streak, either: those goals have come in 22 different games. No player in Spain has been so vital this season.

Cristiano Ronaldo, the league's top scorer, has scored one more goal. He has one penalty more, too. Costa has scored from the spot five times, including against Elche on Friday. He has also missed from the spot four times. Getafe was one of those times, but like the previous three occasions he subsequently scored. That says something about him.

It is the story of his career. Named "Diego" after Maradona, the Brazilian-born Costa first signed for Atlético in 2007 for €1.5m, "virtually off the streets" in the words of the club's former sporting director. There, the football was brutal; Costa recalls it as a war and admits that he missed structure, organisation and understanding. He had played little organised football and Atlético's physical coach, Óscar Ortega, marvels at his strength.

Although he was an Atlético player, Costa had to wait for his chance, and wait and wait. This is not the story of the talented kid who always knew he would get to the top. He played for Sporting Braga, Celta de Vigo and Albacete on loan before joining Real Valladolid for a year. He returned to Atlético in 2010 and was lent to Rayo Vallecano in 2012. This season, for the first time, he knew that he was going nowhere. "I don't like moving house," he says. "And I like the responsibility. I want to feel important." Now, at last, he is.

"He scored the goal of the season, running all the way through on his own against Numancia. He had real power and potential, similar to the original Ronaldo," says his old Celta team-mate Esteban. "But he was still very young and he was a player with great potential rather than a reality yet. It was hard for him: he came to a club that was not going back up, where there was tension and pressure and players went unpaid."

At Rayo Vallecano, his coach, José Ramón Sandoval, called him the "best striker in the world". His Valladolid manager, José Luis Mendilibar, recalls him playing up front "virtually on his own". Costa, he says, had "this fantastic capacity for occupying four defenders on his own. He has this trick of not really looking as good as he actually is."

Mendilibar explains: "He doesn't look particularly quick, or technically that good, but he is far faster and talented than it seems. Sometimes it seems that he is one step away from losing the ball, he doesn't appear to have it under control, but he keeps it and more often than not he finishes. He also had that mala leche." Mala leche means bad milk; edge, nastiness.

"He could be frightening in training," says the Swansea forward Michu, who played with Costa at Celta and Rayo Vallecano. "But he was a sweet bloke. I'm really, really pleased for him. I'm not surprised by his success because he already did a lot of things that made you think he was a player good enough to make it to the very highest level. He's powerful, he's got quality, he works really hard and he scores a lot of goals."

The style has evolved but remains the same: mobile, powerful, cunning, and provocative. He seeks out the defenders and they certainly seek out him. "No opponent ever says: 'Diego, I love you,'" he says. "You get kicked, you hear all sorts of things." Against Real Madrid this season, Pepe blew snot at Costa's face. "That was the only thing that annoyed me," he says. Otherwise, he insists that he does not take what happens on the pitch home with him, which is lucky.

Off the pitch, he says, he is "timid". Esteban agrees: "He's completely different to the image people have of him." On the pitch, it is a battle. Costa is the striker for whom no defender is too big or too mean, no fight to be shirked and no ball lost, for whom every punt is a pass. The first time you see him dribble past a defender, he appears fortunate; the fifth time he does not. He seems to be bundling through, not entirely in control, but he invariably gets there. And when he does he invariably finishes.

Yet if the qualities are the same, the quantity is not. Last season, Costa scored 10 league goals. Before that he had scored 10, 6, 8, 9, and 5 and two of those seasons were in the second division. Fate played its part in bringing him here. Only a knee ligament injury prevented him from leaving for Turkey, every summer he was forced out on another loan, and at the start of last season, despite a successful six-month spell at Rayo, Simeone told him he was not likely to play.

But, the coach says, when pre-season training started "we wanted to kill him: he was flying, flying, flying". He has not stopped since. No matter who, or what, stands in his way.