When I told Rivera what Gossage said about the emotional strain of coming into a game with men on base, he seemed a trifle perplexed — like Mr. Spock encountering the idea of fear. “It’s a thing I can’t control,” he said. “They did it already. I don’t think about it. If you think about it, you’re going to get drained, and you might not do the job. So what is worth to think about? I’ve got to get the guy out that’s at the plate. I can do something about it.” You’re a Yankees rookie, and the season is on the line, and the bases are loaded. Just don’t think about it? Alex Rodriguez, a truly great hitter who has been known to think himself into knots at such moments, may be on to something when he says, “I don’t think he knows what pressure means.”

POWER PITCHERS, who get much of their thrust from their hams, tend to be beefy across the middle. Not Rivera: at six feet two inches, 185 pounds, he is built like a cheetah, an impression reinforced by his smooth skin, his high, sharp cheekbones and his glittering teeth. One morning, when Rivera was preparing to pitch some batting practice, I watched him perform a stretching routine that culminated in a half split, his right leg fully butterflied against the locker-room carpet — more like a dancer than a pitcher. Rivera is an extremely gifted athlete who never seems to lose his balance, even when he has to pounce off the mound to track down a bunt or a slow-rolling grounder. During a game in May, he fired a cutter that broke the hitter’s bat, as often happens, and half the bat came spinning straight at him with the ball bouncing right behind. Rivera leapt straight up, like a kid on a skateboard, came down and speared the ball in the same motion and then threw the man out, a play that so stupefied the Yankees broadcaster Michael Kay that it was replayed again and again.

Image THE GRIP Two fingers across the seams of the baseball. Credit... Barton Silverman/The New York Times

That morning I met with him at spring training, Rivera ambled out to one of the practice fields. Fans gathered along a fence in right field to gawk. Rivera threw to some of the young players with high uniform numbers who would soon be returning to the minors — an experience for them to write home about. Rivera’s mechanics are smooth, simple and unhurried. As he drives forward, his hips rotate counterclockwise, bringing his left knee up just beyond his waistband; his arm comes straight up over his shoulder, and he ends with his hand down by his right foot. “He has real good finish,” Gene Michael says, “a long finish, real good, easy wrist pop.” Goose Gossage says that Rivera, like the ageless power pitcher Nolan Ryan, “throws with the big muscles in his body.” This physiological efficiency explains Rivera’s remarkable durability. And the impression of effortlessness baffles hitters; thanks to his long fingers and loose wrist, the ball seems to explode from Rivera’s hand. After 30 or so pitches, Rivera walked over to the knot of fans and signed whatever they thrust at him.

Everything in Rivera seems to flow in the same direction. “I don’t want to say this like he doesn’t work hard,” Manager Joe Girardi says, “but it’s just who he is. I don’t think he has to think about who he is.” Rivera grew up in Puerto Caimito, Panama, a fishing village where his father worked as a ship’s captain and Rivera, once he was old enough, as a mate. He played baseball, with a flattened milk carton for a glove and a stick for a bat, because he loved it. He just turned out to be much better at it than everyone else. Though we are inclined to think of the Latin American countryside as so grimly confining that young men latch onto baseball out of the desperate wish for salvation, Rivera himself recalls not so much the poverty as the raucous family gatherings orchestrated by his father. His parents were not churchgoers, and neither was he one. Rivera said that he had a born-again experience when he was 21 or 22. Nowadays, he says, his parents have become religious as well.

The Mariano Rivera whom the Yankees saw in 1995 had athleticism, flawless mechanics, velocity and, as baseball people say, makeup. Rivera’s startling performance in the playoffs convinced management that he could be a more powerful weapon coming out of the bullpen than he could as a starter. The team already had a dominant closer, John Wetteland, and as Rivera quickly demonstrated his mastery, Manager Joe Torre made him Wetteland’s setup man. Yankees fans remember 1996 as the year of the six-inning game: if the Yankees were ahead after the sixth, the game was effectively over, because Rivera would pitch the seventh and eighth and Wetteland would pitch the ninth. Like many closers, Wetteland lived on the edge, walking one guy and giving up a hit to another before tugging on his sweat-stained cap and blowing fastballs past the last few batters. Not Rivera: scarcely anything seemed to happen when he was out there. Rivera won eight games and lost three with a sparkling E.R.A. of 2.09. (Anything under 3.00 is considered effective for a reliever.) In 107⅔ innings he struck out 130 batters while giving up 73 hits. (The standard for excellence is striking out one batter and surrendering no more than one hit per inning.) There’s a strong argument that Rivera should have been named the most valuable player in the American League that year, though the award has never gone to a setup man.