NEW YORK — The first image that lingers is a stubborn young man given a lead before he even had to pitch, standing on the mound throwing fastball after predictable fastball. Yordano Ventura has reason to be confident, and reason to be confident in his fastball. Most obviously, it can touch 100 miles per hour, and when it zooms past the bats of the world’s best hitters, he is not above letting them hear about it.

But they say the most compelling reason to be humble is that baseball is a game of failure, and it will beat you down if you’re not careful, and Ventura was not careful when his first six pitches were all fastballs. The last one came in at 96 mph and left David Wright’s bat at 103, not landing until it had cleared the left-field fence by 30 feet or so.

It would not be Ventura’s last mistake, though if it was, the Royals might have been able to avoid being beaten 9-3 by the Mets in Game 3 of the World Series here at Citi Field on Friday.

Ventura is wildly talented, although sometimes the emphasis tilts too much toward wild. He is capable of dominating starts and stretches, but also prone to severe letdowns. Maybe he’ll grow out of that. For now, the Royals just lost a game in which they gave him two leads, and he blew both.

This does not have to be a big deal, of course, the same way that Johnny Cueto’s disastrous start in Toronto did not define the ALCS. The Royals are still in the better position here. Teams with 2-1 leads after three games end have won the World Series 67 percent of the time. The big picture, then, has not changed.

Before this World Series started, there was good reason to believe the Royals would win. They are the more complete team, more balanced, and stronger in the bullpen, which takes on more importance in the playoffs. That remains true.

Before this World Series started, there was good reason to believe the Mets would not go quietly. They have a quartet of terrifically talented starting pitchers, and enough power to be dangerous. That remains true.

The Royals are still in the power position of these playoffs. They lead two games to one, the Mets needing to win three of the last four to keep the parade from going through downtown Kansas City.

But Ventura’s steady stream of mistakes — along with a concerning dip in velocity on that fastball after the first inning — exposed the Royals’ greatest weakness and the Mets’ greatest advantage.

The Royals simply do not know what they’ll get from their starting pitchers, and with the exception of Johnny Cueto, that is truest of Ventura.

He gave up seven hits and five earned runs over 3 1/3 innings, striking out just one. Manager Ned Yost had to call on Danny Duffy to get out of the fourth, which meant using him for just two outs since the pitcher’s spot was due to lead off the next inning. By the time the game was over, the Royals had used every reliever but Wade Davis.

Perhaps Ventura was bothered by the cold weather, or maybe he’s pitching through some type of minor injury or discomfort. At least as of press time, we didn’t know the answer as to why his velocity dipped.

“He doesn’t know why,” infielder Christian Colon said, translating for Ventura. “He just noticed when he came in that his velocity was down when he saw the radar and some video. He says he felt great out there.”

But Ventura’s problems on Friday were not just physical. It’s easy to read the radar gun and see that something’s wrong. Ventura wears his fastball velocity like something of a superhero’s cape, and without it he was left exposed, minimized from a supreme talent to a second-year ballplayer who could not rise to the moment. Whatever the cause of Ventura’s loss of velocity, his mental lapses were perhaps more damaging.

In the top of the third, he hung a curveball — a curveball — in an 0-2 count against pitcher Noah Syndergaard. The pitch got what it deserved, a sharp single to right, and then Ventura put a fastball down the middle that Curtis Granderson slammed into the right-field seats for a two-run homer.

In the next inning, the mental gaffe was even worse. With runners on second and third, Michael Conforto hit a chopper to the right side of the infield. The first day of spring training this year, all 30 teams worked on pitchers covering first base in this situation. They did the same the year before, the year before that, and the year before that. They will do this again next spring.

Ventura, in the noise and chaos of a World Series game slipping away, froze. Hosmer expected Ventura to be covering, and could not beat Conforto to the bag. The Royals trailed by two. After one more batter, Yost brought in Duffy to face Syndergaard. The bats stayed cool, Franklin Morales bombed, and the Mets breezed.

It was the second time this postseason that Ventura had not completed even four innings. In five starts, he has stunk twice, been OK twice, and been pretty good once. That is less than trustworthy, more the volatile first 4 1/2 months of his season than the final six weeks that — along with Cueto’s reluctance to pitch on short rest — made him the Royals’ Game 1 playoff starter.

In the big picture, this is far from major trouble for the Royals. They could have effectively ended the series by taking a three games-to-none lead, but even now, they remain in control. They could still end the series without playing another game in Kansas City, or give themselves two chances to pop champagne at home by winning one of the next two here in New York.

But it is the continuation of a somewhat troubling trend for the Royals: unpredictable starting pitching. Ventura lines up as the Game 7 starter, if the series were to go that long.

Chances are that it won’t. But seeing the Royals’ biggest disadvantage against the Mets exposed is a reminder that they will have to earn this championship.