Daisuke Matsuzaka will be on the mound for Boston tonight. He’s done well in crucial games during his career.

The Providence Journal / GLENN OSMUNDSON

BOSTON — The Red Sox know that Daisuke Matsuzaka will start Game Two of their American League Division Series against the Los Angeles Angels of Anaheim.

They’re just not sure which Daisuke Matsuzaka.

Will it be the one who allowed two runs or fewer in 17 of his 32 starts this season? Or will it be the one who allowed five or more runs in 10 different starts?

Will it be the one who struck out seven or more in 17 starts? Or the one who walked three or more in 17 outings?

Not even the Red Sox know for sure. Matsuzaka’s rookie season was predictably unpredictable.

Perhaps that shouldn’t be a great surprise. The subject of a fierce bidding war, the Japanese import was very good at times, and at times, less-than-average. In some starts, his command was precise; in some others, it was virtually non-existent.

“I think Daisuke’s year was … probably not a surprise the way it went,” said Terry Francona yesterday. “Some ups and downs, some learning. Some different things have been thrown his way. But I think we’re all excited that he’s taking the ball [tonight].”

Call it: the Education of a Rookie. And tonight, begins the Master Class. Game Two will mark his first start against the Angels, and of more significance, his first postseason outing in the major leagues.

The Sox weren’t entirely sure what to expect from Matsuzaka during his first full season in North America and it would be folly to suggest that they know, with any certainty, what they will get tonight.

But if Matsuzaka’s past is any sort of prologue, the results should be favorable. Matsuzaka has shown an ability to rise to the occasion. The bigger the game, the better he’s responded.

He first garnered attention in high school when he pitched Yokohama High School to a national championship in Japan in 1998. In his first start in the famed Koshien National High School Tournament, he pitched a 17-inning, 250-pitch complete game. The next day, he returned to record a save before tossing a no-hitter in the clinching game, striking out 14.

A legend was born, then further enhanced when he shone in two Olympiads. In 2004, he fashioned a 1.69 ERA in Athens. In 2006, he pitched Japan to the championship of the World Baseball Classic, earning MVP honors in the process.

Those performances earned him attention from major league teams. Red Sox general manager Theo Epstein took particular notice, figuring that if Matsuzaka could succeed with the spotlight fixed on him, he could handle the often unforgiving glare of Boston.

“I think it was a factor in determining how he would adjust to performing here,” said Epstein yesterday. “We were looking for any piece of information we could get to see how he performs under pressure. That’s an important element when we’re considering whether someone’s a good fit for us.

“I wouldn’t say it was the biggest [element], but it contributed to the puzzle we were trying to put together. It certainly showed that he has the mentality to deal with the pressure. It certainly bodes well; if he had melted down in every game, we probably wouldn’t have even heard of him.”

As recently as this week, Matsuzaka exuded that same cool demeanor in preparation for his playoff debut.

“The other day,” recounted Francona, “he came out of the bullpen and just looked calm — which he always is — and pretty confident about executing his pitches.”

Tonight’s opponent should help. The Angels are notoriously aggressive and don’t show much interest in working the count or driving up a pitcher’s pitch total. “If he can command and get ahead,” said one major league scout, “he could have some pretty quick innings.”

During the season, Matsuzaka struck out nearly a batter per inning (201 strikeouts in 204 2/3 innings) and that should augur well this month. Historically, power pitchers have enjoyed more success than pitchers who must rely more on location and finesse. That’s why hard-throwing John Smoltz has prospered in the postseason and former teammates, Greg Maddux and Tom Glavine, control specialists, have not.

Like fellow general manager Billy Beane, Epstein views post-season performance as somewhat aberrational, often dictated by luck and circumstance.

“I’m never one to put too much stock in [analyzing] post-season performance,” he said. “October is a really small sample size. A lot of times, it has more to do with timing and less to do with some deep-rooted psychological strain.”

But as the Sox send Matsuzaka to the mound tonight — and have him poised to pitch a series-deciding Game Five, if necessary, Wednesday — one point seems beyond debate.

“If he doesn’t pitch well this postseason,” said Epstein, “we’re going to have a hard time going where we want to go.”

smcadam@projo.com