Tonight, in one of those occasional too-neat coincidences that make you think baseball may be rigged for dramatic effect, Joba Chamberlain will make his first major league start at Yankee Stadium while, a continent away in San Francisco, the Mets’ Pedro Martinez will make his latest comeback from his latest injury. The symmetry would be more than enough on its own without both teams, which opened the year reeling like drunks in a rowboat, showing some real liveliness lately, but there you have it. The great debut at the dawn of what should be a brilliant career and the great return near the end of what has been an unsurpassed one come at points of inflection for two teams that really should be much better than they have been until now.

The real commonality here, though, is just how unfair expectations already are. Neither pitcher will prove a savior in the best case or cost his team the pennant in the worst. The reasons teams win and lose pennants are nearly always too complex to be pinned on any one starter. Still, the story of how, when their teams most needed them, two pitchers rose (or collapsed) and changed the course of a season is just waiting to be written, no matter whether or not it could possibly be true.

In Martinez’s case, the problem is that his long absence — he hasn’t pitched since the fourth inning of the team’s second game on April 1 — hasn’t discernibly hurt the team. The worst construction one can put on the job replacements Nelson Figueroa and Claudio Vargas did is that in their 10 starts and 57.1 innings pitched, they ran up a lousy 4.87 earned run average. This is true enough, but overstates how bad they were, and how much better Martinez might have been.

In Figueroa’s first two starts, he pitched six and seven innings, giving up two runs in each game; in his next two starts, he pitched five-plus innings, giving up three each time. Vargas had two starts in which he pitched six and seven innings while giving up two runs, and two more in which he pitched between five and six while giving up four runs. Only Figueroa’s last two starts, in which he gave up nine runs in 10 innings, were really lousy; otherwise, the two were perfectly creditable, pitching some real gems and keeping the Mets in nearly all their games.

Martinez, who in his brief comeback last fall showed that when healthy he’s still, remarkably, every bit as good as he was in 2006, may well have improved on this. The difference wouldn’t have been more than a game or two at the most, though. Having a great pitcher, even one far closer to the end of his career than to the beginning, is much better than having minor league veterans on the mound, and in the course of four months a healthy Martinez will make a difference in the standings. His absence isn’t why the Mets have been listless until the last week, though, and his presence alone isn’t going to put them over the top. It’s a team sport.

At least the man is in for a relatively easy return; the Giants are the most pathetic team in baseball, and he’ll be facing Barry Zito, whose 1-8 record understates how badly he’s pitched. In record time, he’s gone from sought-after ace to legendary debacle. Chamberlain, in a contrast that adds more of an air of symmetry to the night’s events, will be facing Toronto alpha ace Roy Halladay, who’s been perhaps the best starter in baseball this decade and is having yet another stellar season, completing half his games and striking out seven men for every one he walks.

If you’re going to toss a man in hot water, you may as well toss him in a boiling pot, and there is very little reason to think Chamberlain will be overly affected by the pressure. Still, while unlike Martinez he’s filling in for pitchers who have been truly wretched all year, he’s as badly suited for the role of savior. The heat may not get to him, but circumstances might.

The controversy, first, over whether or not it’s even a good idea to take Chamberlain out of the bullpen isn’t ridiculous. It is true that you can’t protect a lead you don’t have, and that a good starter is a lot more valuable than a good setup man. Still, the late-inning duo of Kyle Farnsworth and LaTroy Hawkins is, as anyone who saw much Cubs baseball during the Dusty Baker era could tell you, almost uniquely flammable. Chamberlain will add real value in the rotation, and starting him is probably the best way to use him, but it’s intellectually dishonest to pretend that some of that value isn’t lost by his removal from tight spots late in close games. The man will likely win games Ian Kennedy would have blown; just as surely, Farnsworth and Hawkins will blow a few Chamberlain would have nailed down.

Equally important, though, is that real life is not a video game, and it’s no certain bet that Chamberlain will hold up as a starter, as he does on PlayStation. In the last decade, not one good starter has moved into the rotation from a short relief role. (Johan Santana is an example of a pitcher who moved from the pen to the rotation, but he had been pitching as a long man.) This is mostly so because pitchers with four good pitches and a frame like Chamberlain’s are used, rightly, as starters from the beginning, but there are no recent and reassuring precedents here.

On the other hand, there are lots of reasons to think Joba might struggle as a starter, from pacing to the fact that he has no real experience setting up major league hitters with all his pitches, working through a lineup several times in a night, or pitching in a big league park at less than full exertion. Chamberlain is awfully talented, but so is Phil Hughes.

If neither man here is suited to wave his magic pitching hand over all the anxieties of his team’s fans, neither are they really suited to do anything less than pitch brilliantly. Caveats aside, the sport is much better with these two healthy and starting; they make for appointment viewing, and even their failures tend to be fascinating. Whatever effect they have in the end, tonight marks the start of brighter times for New York baseball.

tmarchman@nysun.com