Randy Johnson and Mike Mussina have been terrific pitchers in their careers, and Chien-Ming Wang may yet prove to be a terrific pitcher, but if the Yankees are to win it all this season, they will have to be terrific all the time.

The Yankees entered this season with question marks throughout the starting rotation. Despite periodic struggles last season, Johnson was quite good, giving the Yankees 22 quality starts (a “quality start” being a start of six or more innings with fewer than four runs allowed). Can he do it again at age 42? Can Mussina rediscover his health and consistency at 37? Was Wang for real? Would Aaron Small prove to be the baseball equivalent of a one-hit wonder? What if Shawn Chacon showed that you can take the man out of Colorado, but you can’t take Colorado out of the man? Would Jaret Wright and Carl Pavano ever justify the impulsive and foolhardy investments the Yankees made in them?

It’s early to judge, but the answer to the first three questions appears to be a qualified yes. Despite Johnson’s rough outing in Toronto on Tuesday, he has been mostly effective. Mussina has pitched well every time out, including a seven-inning domination of the Blue Jays yesterday, and Wang has done well when the defense has cooperated.

Given the struggles of the rest of the rotation, though, this might not be enough. It is possible for a team to win with just three strong starters; the Astros went to the 2005 World Series on the strength of exceptional performances by Roger Clemens, Andy Pettitte, and Roy Oswalt – and almost no one else. Key word: “exceptional.” The Astros’ aces were the definition of consistency, with each turning in more than 20 quality starts. Because the team’s fourth and fifth starters failed to show up for work about 80% of the time, the Astros had no margin for error on the days their “big three” pitched, and by and large that trio held up its end of the bargain.

This year’s Yankees might be in the same position as the 2005 Astros, but without comparable resources. Part of Chacon’s success last year was a function of good luck on balls in play. Sometimes a pitcher will run into a sustained period of good fortune when the forces of nature direct some balls that would normally go for hits right into fielder’s gloves. Whatever the cause, it’s fickle; good luck on balls in play can sometimes sustain for a season, but rarely for two. In fact, Chacon has traversed the distance from luck to its opposite – bad luck might not be a sufficient description; “cursed” might be better – currently allowing a .381 average on balls in play after allowing a .240 average on batted balls as a Yankee last year. The league average on balls in play has stayed in the vicinity of .300 for more than a decade.

Small should return soon from his strained right hamstring, at which point he will have to start living down his pre-Yankees 5.49 career ERA. He also caught a break on batted balls last year, with a .276 average allowed. Small strikes out very few batters, so his success is dependent on balls finding fielders instead of holes.

Pavano has a bad back, and for all the anticipation focused on his return, the fact is that he may never be healthy enough to pitch at full strength, or whatever level of competence the Yankees were assuming when they signed him. Pavano’s is an old story – a pitcher with a high ceiling whose body never let him achieve what was expected of him. He has just one solid season under his belt (2004, when he went 18-8 with a 3.00 ERA in Florida), that year having been achieved at a rare moment when the pitcher was healthy and in the right ballpark in the right league.

Jaret Wright may still throw hard enough to be an adequate middle reliever (he was routinely hitting the mid 90s in Minnesota this week), but the scant evidence that can be garnered from his appearances thus far is that 30 or 40 pitches may now be his limit.

So this is depth, in this case not so much an abundance of quality arms as an abundance of arms. In Wright’s case, it might not even be an arm at this point. That puts the focus back on Johnson, Mussina, and Wang. Unless the Yankees have the depth to make a deal for a Dontrelle Willis later in the season – and it’s doubtful that they do given the packages the Marlins received for their other discards – the rotation shortfall may not be solvable from within other than by the big guys taking a step forward. In this sense, Johnson’s last two starts – a strong but shortened outing followed by a buffet dinner for the Blue Jays – do not bode well.

Last season, Clemens, Pettitte, and Oswalt had 78 quality starts in 100 tries. The Astros’ other starters chipped in another 18, for a major league-leading total of 96. The Yankees had 78 quality starts in total, and they were more diffuse, with Johnson posting 22 in 34 starts and the rest spread among the other starters. That was enough last year, and could be again, but we won’t know for several weeks whether the top three will show that kind of consistency.

Failing that, the Yankees could try to score even more runs, bludgeoning opponents in starts where they don’t get good pitching. That’s an approach that seems doomed to fail should the team make the playoffs, but getting to the playoffs is the issue now, not winning them. Fortunately for the Yankees, getting more offense is an easy fix, involving giving the designated hitter job to an actual hitter instead of Bernie Williams, an ex-hitter. In what looks to be another season of improvisation and prayer, every little bit helps.

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