When the Mets play well in the second half, they generally make the playoffs.

The Mets have reached the postseason nine times, never producing worse than a .588 winning percentage after the All-Star break in any of those years. Nine of their best 11 second halves led to the postseason. One of the two that failed, the 1985 Mets, actually had the NL’s second-best overall record, but in a wild-card-less era didn’t win the East.

The Mets have never climbed above a .700 second-half winning percentage, the high of .671 coming 50 years ago, the sainted 1969 squad. The 2019 Mets begin a nine-game homestand Tuesday with an MLB-best .706 win percentage (24-10). The Yankees are second at .684 (26-12).

The Mets have generated this success by clobbering the soft underbelly of their schedule. The homestand is a degree-of-difficulty pivot with the Indians, Braves and Cubs at Citi Field. But beating up weaklings is central to the formula for strong second halves as laid out by an expert on the subject.

Billy Beane is the Athletics’ executive VP of baseball operations, and in his two decades-plus running Oakland’s baseball department, his clubs have become masters at starting slow and finishing terrific. The A’s have the majors’ seventh-best record of the 2000s, but the third-best after the All-Star break. Oakland has five of the 30 best second-half records this century — the Yankees with three have the next most.

One of the five came last year, when the A’s went a major league-best 42-23 after the All-Star break to rally to a wild-card game that they lost to the Yankees. And they are at it again in 2019, going 21-12 (.647), including taking three of four from the Astros over the weekend prior to hosting the Yankees beginning Tuesday.

So I contacted Beane, who gave me a general roadmap of what he thinks is important to second-half success, which includes:

1. At worst, survive the first six weeks of the season at .500-ish. If a team is around .500, it can launch into competitiveness. And the six-week period provides the first barometer of what the team’s true strengths, needs and injury situations are.

2. Disregard outside noise. In 1999, his second year on the job, Beane was assailed for trading his ace, Kenny Rogers, and closer, Billy Taylor, to the Mets in separate deadline deals. But Taylor brought in a better closer, Jason Isringhausen, and the money saved by the Mets taking on all of Rogers enabled Oakland to add Kevin Appier, Omar Olivares and Randy Velarde. The A’s went 44-31 in the second half and won 87 games. They missed the playoffs, yet Beane was informed about following the concepts of his department and, vitally, not surrendering.

3. Keep trying to get better with not just big moves, but small ones. Every win matters. One of Beane’s tenets is not to tank, but to use all of his small budget to try to win as much as possible. The belief system creates a group mindset that has helped those second-half surges.

4. That mindset means more when so many teams are not emphasizing winning. In the second half, the plight of those downtrodden teams worsens because of attrition or seller trades or injuries or just the bad mojo brought by an environment in which winning is not prioritized. This has become more pronounced in recent years with teams trying to follow the Cubs/Astros model of sinking to the bottom as a way to rise to the top.

It has created super teams and super-bad teams and fewer teams willing to accept the middle. But for those in the middle who do not surrender there are gift wins available as the bad teams grow worse. The A’s regularly capitalize upon this process. And this season it defibrillated the Mets, who all but conceded in mid-July, when GM Brodie Van Wagenen mocked his own “Come and get us” bluster, before a surge led the Mets to buy instead of selling at the deadline. They are the accidental contender.

Bad teams often worsen as the season progresses. There were eight playing below .400 in the second half plus the Mariners and Royals were barely above that. That is a third of the league. The Mets have played 21 second-half games against members of that Woeful Ten, going 17-4.

The disparity distorts. There are just so many easy wins on the schedule. The Mets (.706), Yankees (.684), Indians (.649), Dodgers (.647), A’s (.636) and Astros (.629) were on pace to have six of the best 50 second halves this century.

Can the Mets continue that with their schedule toughening and just four games remaining (vs. Miami) against the Woeful Ten? At minimum, they have capitalized enough to make their second half relevant.