In a year in which most everything that could go wrong has gone wrong for the Yankees rotation, the most pleasant surprise has been the resurgence of Orlando Hernandez.

I’m surely not the only one who found the sight of El Duque pitching his home games beneath the orange Kevlar roof of Montreal’s Olympic Stadium last year to be something of a slight to his dignity. And I’m just as surely not the only one glad to see him back in Yankee pinstripes and dominating his opponents.

Tonight’s game against the Rangers is a key one for both Hernandez and the Yankees. With the AL East title more or less wrapped up, Joe Torre’s biggest concern these days is getting his rotation sorted for the playoffs.

Javier Vasquez is the only reasonably sure bet to be both healthy and effective come October. Assuming they’re able, Kevin Brown and Mike Mussina will be pitching no matter how effective they are over the last six weeks of the season. This leaves Torre with a choice among Hernandez, Tanyon Sturtze, and former 20-game winners Jon Lieber and Esteban Loaiza for the fourth slot in the rotation.

Torre’s loyalty, the other pitchers’ poor performances, and Hernandez’s legendary post-season exploits probably make him the favorite to grab a spot. He’ll have to earn it, though.

El Duque’s statistics this year look great – a 2.08 ERA,and a 47/16 K/BB ratio in 39 innings – and he has certainly looked like his vintage self on the mound, baffling hitters with tight and loose breaking balls, perfectly spotted fastballs to both sides of the plate, and ludicrously slow changeups thrown in counts when changeups are never thrown. But he’s pitched mostly against weak competition, and the statistic Torre is probably keeping the closest watch on is his pitch count.

Of the three teams Hernandez had faced going into last night’s game, two – Detroit and Baltimore – have good offenses. In each of those starts, he went five innings and gave up three runs. Partly, that was because those teams laid off a lot of his dead-fish pitches, making him throw the ball over the plate more, but the outcome was also affected by Hernandez going on the mound without his best stuff.

Toronto, against whom he’s made three starts, has one of the worst offenses in the league.He’s done well against them, not allowing a run in 17 innings over three appearances, but there’s a great deal of difference between throwing eight scoreless innings at Toronto and doing so against a team like Boston or Cleveland in a playoff game.

That’s why last night’s start was crucial. In their home park, the Rangers field a devastating offensive team. Their OPS in the Ballpark at Arlington is .856, and they have good left-handed hitters like Hank Blalock, Mark Teixeira, and Brad Fullmer in the middle of their lineup.

Lefties have always hit Hernandez much better than righties, as his deceptive delivery is much less so against them. While bad start last night wouldn’t have meant that El Duque’s return is a mirage, the start he had goes a long way towards showing that he really is back and that he really can be relied upon in October. He made Blalock and Teixeira chase balls they’d usually sniff at, and once he realized that balls weren’t going to start flying out of the yard he left the ball up and let the outfield do his work for him. It was a very encouraging performance.

Aside from the quality of his pitching, though, there is another factor to be watched here: his health. The hamstring strain that caused him to leave his second Toronto start early is the least of the problems, the main one being the shoulder injury that recurred throughout his first stint in New York and cost him most of last season.

The Yankees have handled him carefully, not letting him go much past 100 pitches in any of his starts thus far. That’s worked against the Blue Jays, but it’s left him looking like a five-inning pitcher against the Tigers and Orioles.

Given the shaky health of the rest of the rotation,if Hernandez can’t get through a good lineup efficiently enough to pitch six or seven innings with his 100 pitches,it may be wiser to give playoff starts to Lieber or Loaiza. If nothing else, they can be relied upon to rest the bullpen when they take the mound. If they fail,Torre would have El Duque at the ready.

While the injury concerns are real, I think that Hernandez will show over the next few weeks that he has returned to form. There doesn’t seem to be much wrong with him physically; in any case, his effectiveness has always been more the result of intelligence and craft than physicality.

Along with his wide array of pitches, deception, poise under pressure, and ability to adjust to what hitters are trying to do against him, Hernandez has a gift for adjusting to what he’s capable of doing on any given day. That didn’t come through against Detroit and Baltimore,but given time to work off some of the rust that comes with only having pitched sporadically for the last couple of years, I think it will.

Certainly last night he didn’t have his best stuff, but in circumstances in which he had every reason to fail, he made a very good lineup look foolish.There are very few pitchers today who can so precisely calibrate the speed of their changeup to how hard they’re throwing; I’ve seen El Duque come out to the mound with absolutely nothing and get hitters out with sub-60 mph eephus pitches. He’s still one of the smartest, gutsiest, and most collected pitchers in the game, and no matter how well he does over the next few weeks he’d be my first choice among Yankees to pitch a must-win game.