Fans cheer during the sixth inning of Game 5 of...

Fans cheer during the sixth inning of Game 5 of the World Series between the Kansas City Royals and the New York Mets Sunday, Nov. 1, 2015, at Citi Field. Credit: AP / Charlie Riedel

October already feels like an eternity ago. The 2015 season? A faded, wrinkled memory. For as much as baseball relies on its history and clings to the past, no sport looks forward to a fresh start with such boundless hope or the same powerful thirst for renewal.

Take the Mets, a team that watched a dream year abruptly end as the calendar flipped to November, its title chances undone by Matt Harvey’s unbending will and the fickle aim of Lucas Duda’s right arm. Just as no one predicted the Mets’ unlikely march to the World Series, who could have imagined Jeurys Familia blowing three saves once they got there?

For the Yankees, a wild-card entry, the playoffs lasted a single night, a total of nine innings. While there was some satisfaction in snapping a two-year postseason drought, it was over so quickly that only the bad taste lingered.

Every summer, the Yankees resurrect the dynasty years with another inductee to Monument Park, but the members of the Core Four are wall ornaments now as the Bronx faithful waits for its next incarnation.

This isn’t a time to dwell on the failures, however. April is a month for skyrocketing optimism, the belief that anything is possible, with October the ultimate goal.

Over in Port St. Lucie, where the Mets spent much of spring training ogling Yoenis Cespedes’ car show or riding the slugger’s horses, the talk wasn’t so much about returning to the World Series as it was finishing the job in 2016.

“I definitely think there’s a little more expectation,” Jacob deGrom said shortly after his arrival in Florida. “And I think we expect to make it back to the World Series and win it.”

Left unsaid: It’s not that easy.

At first glance, the Mets’ roster is nearly identical to the one that conquered the Nationals, outlasted the Dodgers and swept the Cubs en route to the Fall Classic. By increasing the payroll to $140 million, the highest it’s been in five years, the Wilpons also upped the ante. In selling more tickets, the Mets have convinced their fans to buy into the dream, and delivering on that pledge often is tougher the second time around.

“There’s a lot of twists and turns along the way,” Sandy Alderson cautioned early in camp. “But just being able to start from that position, as opposed to where we have been the last couple of years, that’s a great feeling.”

Despite the rosy projections, the Mets enter the season with a few questions still unanswered: The long-term prognosis for David Wright’s chronic back condition. DeGrom’s missing velocity in his Grapefruit League starts. Matt Harvey’s late ERA spike coinciding with a bladder infection that put a brief scare into Mets Nation. And what of the wobbly bullpen bridge to Familia?

As for the level of concern, using a scale of “relax, it’s spring training” all the way up to “dang, they’re doing it to us again,” we’d put the Mets’ needle closer to the former. Is there a better test out of the gate than a World Series rematch with the Royals? Two games in April have never felt so crucial, so pivotal to a team’s psyche, to say nothing of the Mets’ jittery fan base.

The Yankees get their own playoff rematch on Opening Day in the Bronx, as they’ll face the Astros. But they seem to have less to prove, particularly as they wait for their controversial offseason prize, Aroldis Chapman, to return from a 30-game domestic violence-related suspension. That means the true wow factor for the Yankees, the shutdown trio at the bullpen’s back end, won’t be performing together until early May.

“There’s no one walking around that does what he does,” catcher Brian McCann said of Chapman’s lightning fastball.

We know another Yankee who fits that description, albeit for different reasons. Chapman’s delayed arrival leaves the stage primarily to Alex Rod riguez, now back in the fold as the only other player in pinstripes capable of generating legitimate heat.

If there was any doubt, A-Rod commanded the back pages this spring just by suggesting he will retire after the 2017 season, at the end of this Yankees contract, at the age of 43.

What many people already assumed, A-Rod transformed into breathless copy, and his pursuit of Babe Ruth on the all-time homer list this season will be must-see TV.

With so much effort wrapped up in Chapman and A-Rod drama, we tend to overlook the Yankees’ real chance in the AL East, with the usual caveat of staying healthy. The difference between the rotation staying intact or crumbling could translate into a 20-game swing, from 90 to 70 wins, or somewhere in that neighborhood.

The promise of newcomer Starlin Castro is offset to a degree by the older, more fragile stars such as Carlos Beltran and Mark Teixeira. The Yankees’ lineup, when complete, has the ability to be a very dangerous group. But we’ve been tricked before into thinking that’s possible over a 162-game season.

Then again, there’s no point in worrying about that now. Forget all that happened yesterday. There’s new memories, and another long season, ahead.

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