Standing inside London’s Finsbury Park in late June, Mariano Rivera was asked to describe his Hall of Fame career in one word.

As he surveyed a group of youth who had finished learning from Rivera and other Yankee greats at a clinic, Rivera simply said, “Amazing.’’

Quick.

Accurate.

Just like how he worked the ninth inning.

My first year at The Post was 1997, the season Rivera was installed as John Wetteland’s replacement. The Yankees had seen enough of Rivera on the way to the 1996 World Series title — of which Wetteland was the MVP — to let Wetteland split via free agency.

I spent 17 years being around the best pitcher who ever took a big-league mound.

Not the best closer. The best ever.

You don’t need to be reminded Rivera is the all-time saves leader with 652, a mark that will never be surpassed. And there are 42 saves in the postseason. Instead, this is a glance behind the velvet rope.

When the Yankees were in the midst of winning three straight World Series titles (1998-2000), Reggie Jackson described what the stoic Rivera looked like on the mound in big moments.

“Death on the cover of GQ,’’ Jackson said in the only way he could — dramatically.

Rivera was certainly death to hitters, with a cut fastball that killed bats in the hands of left-handed hitters.

“They can’t keep the ball fair if they hit it,’’ fellow reliever Mike Stanton said of Rivera’s cutter, which was his calling card and the reason he is in the Hall of Fame — the first, and possibly last, player to appear on all ballots.

Ask Ryan Klesko, a left-handed-hitting Braves first baseman in the 1999 World Series who was fortunate he walked out of Yankee Stadium with his fingernails intact after Rivera turned his lumber into kindling wood multiple times.

As Rivera aged he accepted the responsibility to mentor younger pitchers. Every spring before the exhibition games started, Rivera gathered the young arms in the Legends Field (later renamed George M. Steinbrenner Field) dugout to talk baseball and life. Two who owe their big league careers and World Series rings to him are Ramiro Mendoza and Edwar Ramirez.

Far too often in this business a player gets slammed for not talking to the media. Rivera never gave anyone a reason to bruise him for that.

A perfect ninth to close out a World Series or the night he broke Luis Gonzalez’s bat and lost the 2001 World Series in Phoenix, Rivera was available.

That night, the media had started to exit a very grim clubhouse. The only noise for most of the postgame session was the shower water. Now, that was muted. The Post’s Joel Sherman heard that legendary trainer Gene Monahan addressed the team before the devastating loss and told me. Players were headed into a Phoenix night, and Rivera was among the few who hadn’t left the clubhouse.

He answered questions about Gonzalez’s bloop hit over the Yankees’ drawn-in infield until the last reporter was gone. Sitting alone at his locker, he was approached by The Post and asked what Monahan’s message was.

Without hesitation he said, “He told us we had a great team here.’’ Nobody would have thought anything about it had Rivera said he had enough. But he didn’t, even after being one out away from a fourth straight World Series title.

Death on the cover of GQ had a sense of humor, too.

One winter he went home and didn’t throw until arriving in Tampa. The first bullpen session was comical in the fact that Rivera, who could hit a gnat in the butt with a baseball, was all over the place.

The next day, The Post’s account of the exercise compared Rivera to Mitch Williams, a gas-throwing lefty reliever for the Cubs and Phillies known for severe wildness.

Asked about the story the next day, Rivera questioned a group of writers, “Who wrote that?’’

“That would be me,’’ I said to Rivera, who smiled.

“OK. Tomorrow you come down to the bullpen to catch and I will take two balls and break all 10 of your toes,’’ Rivera said through a serious face that broke into a grin.

There was no trip to the bullpen.

The skinny kid from Panama called the bullpen his home. Now he adds a wing to it in Cooperstown.

Standing in Finsbury Park on a day made for baseball and a long way from The Bronx, Rivera selected a word as perfect as the cutter he rode to Cooperstown: amazing.

And nobody can disagree.