You can’t measure immortality in a boxscore. So for Roger Clemens, striking out 20 batters in one game was the least of his accomplishments.

On that night 17 years ago, what Clemens truly did was immerse himself in legend by doing a simple thing – he performed beyond the realm of possibility.

“One of those things you dream about,” former Red Sox catcher Rich Gedman calls it, “and say it’s never going to happen.”

It happened. Welcome to April 29, 1986.

At Fenway Park that night, all the elements collided for one brush with destiny. The Mariners were in town, a collection of free swingers who amassed strikeouts like spare pennies. Temperatures, meanwhile, topped out in the 40s. You think it’s scary to step in against a flamethrower? Try it on a cold evening.

So it was when Seattle’s Spike Owen came up to led off. In fact, Owen was quite familiar with Clemens, having played college ball with him at Texas.

Clemens’ first pitch brushed his old buddy off the plate. His second one knocked Owen to the dirt.

“That certainly got my attention and possibly everybody else’s,” Owen says. “[My teammates] were saying, ‘These guys were friends!’ “

And in some ways, the intimidation battle was already over. Throwing all fastballs, Clemens struck out the side – Owen, Phil Bradley, Ken Phelps, all down swinging.

The next inning, Clemens fanned two more. Meanwhile, over at first base, Boston’s Don Baylor realized something was happening. He had seen Clemens’ fastball exploding and would later say that the pitcher’s stuff was “electric.”

“To me,” Seattle’s Bradley says, “he was throwing as hard as anybody ever threw.”

After three innings, Clemens had six strikeouts and hadn’t allowed a hit. He had thrown all fastballs and in fact, for the night, Gedman says 80 percent of the pitches were heaters. The rest were all sliders.

Except for one.

In the fourth, Owen led off, Clemens threw a curveball and Owen smacked it for a single. Running down the line, Owen screamed at Clemens, “You dumb son of a [bleep].”

“You’re throwing about 100 mph and you’re trying to trick somebody!” is how Owen remembers it, laughing.

Message delivered. After Owen’s single, Clemens went back to business, striking out the side. He did likewise in the fifth and then fanned Dave Henderson and Steve Yeager to open the sixth. Eight straight punchouts.

“Nobody touched the ball,” Baylor says. “Guys were throwing the ball around the infield and that was it. Strikeout, strikeout, strikeout.”

By that point, Clemens’ buzz was swirling around Boston. The 13,414 fans moved closer to field level. Six thousand tickets – a Red Sox record – were sold after the game started.

After striking out two in the eighth, Clemens had hit 18. In the dugout, pitcher Al Nipper approached Clemens and told him what he was on the verge of. Clemens had no idea.

Owen led off the ninth and went down swinging, tying Clemens for the MLB record. That brought up Bradley, whom Clemens promptly sat down with a called third strike, a fastball on the inside corner, for the magic number.

“I still say the last pitch was inside,” Bradley says.

Clemens still had a chance to reach 21 strikeouts. But with two strikes, Phelps grounded a fastball to short.

Twenty would have to do. That, and immortality.

April 29, 1986 at Fenway Park

Red Sox 3

Mariners 1