Sunday’s 5–4 loss to the Oakland A’s represents the best and worst of what the 2007 Yankees have to offer. That on this particular occasion the “worst” was embodied by Mariano Rivera added painful irony to what is shaping up to be a complex, difficult season.

The best in this case was Andy Pettitte. Though not credited with a win, he pitched his second, strong game in a row, throwing seven innings and allowing just two runs, one earned. His ERA stands at a sparkling 1.50.

There is a whole season yet to play, and at its end, Pettitte’s record may look very different than it does now. Pettitte’s arm is always day-to-day, and that has led to great inconsistencies. Last season, there were two Pettitte’s: the evil Pettitte, who pitched before the All-Star break and went 7–9 with a 5.28 ERA, striking out 6.8 batters per nine innings, and the good Pettitte, who pitched after the break, going 7–4 with a 2.80 ERA and striking out 8.3 batters per nine. If not for the manifestation of this version of the pitcher, Pettitte would now be pitching for Houston — or not at all — regardless of what he had done for the Yankees in the past.

Given that the Yankees have been the most dominant team in baseball for the bulk of the last 80-plus years, Pettitte’s contribution to that record has been disproportionately historic. The Yankees have frequently fielded great teams with great pitching, but haven’t necessarily had great pitchers. More accurately, they haven’t had starting pitchers who had the kind of sustained greatness in pinstripes that, say, Warren Spahn, had with the Braves.

The franchise leader in wins is Whitey Ford, with 236. Ford was an all-time great pitcher and an exception to the rule, as was, perhaps Red Ruffing (231). The two are followed by a parade of pitchers who were dominant at times but were inconsistent or prone to injury. Ron Guidry might have had the single best season by a Yankees pitcher in 1978, but taken in its entirety his career totals seven or eight strong seasons. Allie Reynolds, Vic Raschi, and Ed Lopat, the great rotation of the late 1940s and early ’50s, came and went quickly. Waite Hoyt burned out early. Lefty Gomez had burned his arm out by the time he was 30.

That makes Pettitte, almost by default, one of the most consistent and longest-lasting pitchers in team history, even given his threeyear sojourn in Houston. With 150 wins, he ranks ninth on the team list, and will soon break into the top 10 in innings pitched as well. With 16 wins this season he will pass Mel Stottlemyre for sixth on the franchise list. Although Pettitte has rarely, if ever, rose to the dominance of a Guidry or a Ford, he has pitched well enough to win for nine seasons, and it appears he will now add a tenth.

Of course, if Pettitte is to pile up a high victory total, he’ll need some help from the bullpen, and given the pattern of the season’s first 11 games, there may not be much of a bullpen left to do that. Mariano Rivera blew his first save opportunity of the season on yesterday, but there’s more — compared with the other denizens of the bullpen he’d hardly been used. Up to and including yesterday, Rivera and Sean Henn had appeared in five games; Kyle Farnsworth and Brian Bruney in six; Mike Myers in seven, and Luis Vizcaino and Scott Proctor in eight games each. No one expects the starters to pitch complete games, but Joe Torre is risking making first-half burnout a roster-wide affair.

There’s no such thing as “pace” with relievers — they can always take a few days off — but with pitchers like Proctor and Vizcaino there’s no reason to believe that they’ll be resting any time soon. If either appears in the Yankees’ twelfth game, they’ll have pitched in an even nine out of 12, or 75%. If the pair could somehow sustain that rate over a full season, they’d show up in 120 games each. It’s far more likely, though, that their arms will fall off long before then.

The Yankees have had some difficult pitching circumstances to deal with — in-game injuries to starters like Mike Mussina, extrainnings games, short starts — but it seems unlikely that the need to call to the bullpen will decrease. The solution may not be more relievers, but relievers with more flexibility than one-batter and one-inning pitchers of the sort Myers and Farnsworth can provide. In other words, the team needs one more traditional “long” reliever. The Yankees have the pitching depth to achieve this, but it’s not clear that they’ll bother until after it’s too late to save the staff from overuse.

Mr. Goldman writes the Pinstriped Bible for yesnetwork.comand is the author of “Forging Genius,” a biography of Casey Stengel.