One of the great mysteries of Omar Minaya’s tenure as general manager of the Mets has been the ease with which he’s found gold amid garbage. John Maine and Oliver Perez, who were acquired in exchange for essentially nothing and look capable of anchoring the starting rotation for the next five years, are the best examples, but they’re not the only ones. Orlando Hernandez seemed finished before Minaya brought him to New York last year and has been a fine no. 2 starter since then, and Jorge Sosa has started his Mets career more than credibly.

Another of the great mysteries of Minaya’s tenure has been his bizarre fixation on pitchers with absolutely nothing left. From Jose Lima to Chan Ho Park, the Mets have, over the past few years, seemed to take pride in handing the ball to some of the very worst pitchers in the major leagues, pitchers so bad no one was aware they were still playing professional baseball.

This raises a question: How can the same team that made the Perez deal have given Lima, possibly the worst pitcher in major league history, four starts last year? Is Minaya the shrewd dealer who swapped out the well-paid, mediocre Kris Benson and his obnoxious wife for Maine, or the oblivious no-goodnik who looked at Park’s crummy statistics and batting practice fastball and said, “Now there is a New York Met?” Obviously he’s both, and just as obviously, the good outweighs the bad. What’s interesting, though, is that the bad deals and the good deals alike have a lot in common.

If you draw up a list of the less heralded starting pitchers Minaya has acquired — say, everyone so far mentioned here, plus Kaz Ishii, Dave Williams, and Aaron Sele, who started for the Dodgers last year and might end up taking some starts for the Mets in different circumstances — some obvious commonalities jump right out at you. The first is that Minaya likes to buy low. These pitchers had some wretched earned run averages when the Mets acquired them. Maine was coming off a season in which he’d pitched 40 innings with a 6.30 ERA. Perez had a 6.63 ERA when the Mets traded for him. Williams had a 7.20 ERA. At the absolute best, these pitchers were coming off tolerably mediocre performances. More often, they’ve been outright awful.

The second is that those bad ERAs usually masked recent histories of adequacy, and even excellence in some cases. Maine and Perez, in particular, were clearly talented young pitchers, but every one of these starters had done at least something well recently enough to be worth a chance. Even the historically terrible Lima could be relied on to take the ball, if nothing else, and that has some value in its own right, as the Yankees could tell you.

The third similarity is that in most cases, those bad ERAs weren’t as bad as they looked. When Minaya traded for El Duque, for instance, he had a 6.11 ERA, but he also had a good strikeout-to-walk ratio, and his statistics were generally more in line with those of a pitcher with a 4.60 ERA — not great, but useful.

The strongest commonality, though, is that without exception, these were all flyball pitchers — as is Pedro Martinez, the one starter for whom Minaya paid a lot, and one who of course pitched at a Cy Young level in 2005, coming off of the worst season of his career. Most of them surrendered an extreme number of flyballs.

What’s unusual about this is that ballclubs generally prefer groundball pitchers, because groundballs never go over the fence. In any given year, a ranking of the top groundball pitchers will usually be a list of some of the best pitchers in the game, with a few very good pitchers in there as well, while a ranking of the top flyball pitchers will be an eclectic list of the excellent and the terrible. No one goes out and rounds up pitchers who keep the ball in the air while eschewing those who kill worms, but that’s just what the Mets are doing.

If you think about it, this is of course exactly what the Mets should be doing. Not only do flyballs die in Shea Stadium’s spacious outfield, but the Mets play a disproportionate number of games in the pitcher’s parks of Washington, Miami, and Atlanta, all places where it’s hard to hit a home run. Further, with Carlos Beltran in center field and superlative defenders like Endy Chavez and Mike Cameron on the roster, the Mets have featured excellent outfield defense for the past few years, even with the likes of Victor Diaz and Moises Alou staggering around out there. Picking up potentially useful pitchers who throw the ball over the plate and get it in the air is exactly how the Mets should be filling in the blanks in the rotation; they’ve been better positioned to get value out of that class of pitcher than pretty much any other team in the game.

Looked at this way, it makes perfect sense that the Mets have had the horrid to go along with the good. To find pitchers like El Duque, who are unusually equipped to take advantage of roomy parks and quick fielders, you have to suffer through a few pitchers like Park and Lima. It isn’t always pretty, but overall this approach has paid off pretty well for a team whose starting pitching has over the last few years been a lot better in the real world than it has been on paper.

Before the season, no one could figure out how the Mets were going to get anyone out; now, they’re first in the league in starter ERA. It takes a bit of luck to turn up a tandem like Maine and Perez, but it takes some smarts to get lucky in the first place. Tip a cap to Minaya and his staff; they’ve earned it.

tmarchman@nysun.com