“I’m just going to keep trying to make the good pitches,” Mr. Perez had said, standing by his locker. “I feel good right now. The key is to be consistent.”

Throughout the 25-year-old lefty’s career, one which has had more improbable peaks and valleys than most players' far older than he, that consistency has been elusive.

Mr. Perez, a soft-spoken, highly likeable native of Mexico, struck out 239 batters in 196 innings and pitched to a 2.98 ERA for Pittsburgh in 2004. By 2006 he was a throw-in to an under-the-wire trade deal with New York.

But even though his reputation for volatility has followed him to the Mets, Mr. Perez has become a markedly different pitcher in 2007. He’s done so by throwing strikes.

Even in his dominant 2004 campaign, he walked nearly four batters per nine innings. By 2005-2006, that rate shot up to nearly six per nine innings.

For most pitchers, such wildness means a demotion to the minors, or worse. But lefthanders are in short supply anyway. And lefties who, like Mr. Perez, have a mid-nineties fastball, a devastating slow curve (which Mr. Perez calls a “slow slider”) and a drop-off-the-table hard slider, tend to get second and even third chances.

The hurler entered 2007 on the heels of an unlikely performance, having earned the nod over the ineffective Steve Trachsel to start Game 7 of last year’s National League Championship Series. The Oliver Perez that Mets fans have been fortunate enough to see this season was on display that night. He pitched six innings and allowed just one run (aided by a miracle catch from Endy Chavez). But he also threw 61 of his 88 pitches for strikes—nearly 70 percent. For comparison, Greg Maddux, the premier control artist of the last 15 years, is at 70.1 percent so far this season.

This was not a pitcher toning down his wildness, overcoming uneven control with unhittable stuff. This was a pitcher in total command.

His 2007 season has frequently been thrilling to watch, and he entered Friday night’s game having allowed 14 walks in 42 innings; just three per nine. He’d thrown more than 60 percent of his pitches for strikes in six of eight starts, and more than 6 percent in half of his outings.

Those season totals are even more astounding considering that they include his disastrous start on April 6 against the Phillies, which featured what can only be considered a complete breakdown. With two outs in the third inning of that game, he allowed the following: single, walk, walk, walk to force in a run, walk to force in another run, hit batter to force in a third run. He was then lifted by manager Willie Randolph.

He threw just one called strike during the whole sequence. With his history, and reputation, people feared the worst. Rick Ankiel, a Cardinals phenom whose control mysteriously disappeared during the 2000 playoffs, never to return, was a recurring comparison. Fears abounded that his breakdown was not simply mechanical, but mental.

Critics were quick to compare Perez to Nuke Laloosh, the flame-throwing character in the film “Bull Durham” reputed to have “a million-dollar arm and a ten-cent head.”

But if Mr. Perez had been guilty of overthinking or just losing control of his game, he bounced instantly and to ruthless effect. In his next two starts, against the Braves and Nationals, he struck out 18 in 13 2/3 innings—and did not walk a batter. (To return to the gold standard of control, Greg Maddux has just two zero-walk starts all season.)

Mr. Perez threw first-pitch strikes to nearly every hitter, and during the Braves outing, he had a streak of twenty consecutive strikes.

“I’ve simply gotten more and more confidence as the season has gone on,” Mr. Perez said on Thursday in the clubhouse. “I’m going to go out and feel good about my next pitch, and focus on that pitch. I don’t want to just strike out guys. When you get to this stage, you see that velocity isn’t so important.”

The strikeouts have been coming in bunches nonetheless. He’d fanned a batter an inning entering Friday’s game, something no Mets starting pitcher had done over a full season since David Cone in 1991. Which should go some way towards explaining the unmistakable hint of swagger the team now assumes when Mr. Perez takes the mound.

“I think Game 7 last year was Oliver’s introduction to Mets fans,” Mets General Manager Omar Minaya said before Friday’s night’s Subway Series opener. “Maybe tonight is his introduction to Yankee fans.”

Of course, that confidence may also have had something to do with the relative positions of the two New York teams at the moment.

While the Met rotation, driven by Mr. Perez and another young, out-of-nowhere star, John Maine, few Yankee pitchers in 2007 have even achieved mere competence, and the ones who have pitched well--Andy Pettitte and Mike Mussina--are a lot closer to the ends of their careers than the beginning.

And by contrast with the Mets’ National League-best 26-14 record going into the weekend, the Yankees stood at 18-21, 9.5 games behind the Boston Red Sox.

“This is a new era for us,” Mr. Minaya said of the Mets’ recent success. “Oliver represents that as a young, exciting player.”

Once the game started, it became clear that Mr. Perez didn’t have his best stuff.

On the third pitch of the game from Mr. Perez, Johnny Damon lined a single to left field. But he was thrown out trying to stretch it into a double, and Mr. Perez found himself with one out and nobody on. He promptly threw ball one to Derek Jeter, and after a strike, three more out of the zone. He fell behind Alex Rodriguez 2-0, but induced a groundout. He fell behind Jorge Posada 2-0 and eventually walked him. He came back to get ahead of Hideki Matsui, and was fortunate that his line drive was hit right at second baseman Damion Easley.

This was not in-command Oliver Perez, and Mets fans had reason to be worried. It was the form he had displayed just twice this season: during the Philadelphia debacle, and last week in San Francisco, when a pair of errors led to a six-run inning and his early departure.

Mr. Perez got through the second and third innings unscathed, but he was frequently behind in the count, even to pitcher Andy Pettitte, before coming back to record his only early-inning strikeout.

In the fourth, it looked like the control problems had caught up to him. With one out, he fell behind Jorge Posada 2-0, and one pitch later allowe
d a single. After falling into a 3-1 hole to Matsui, his next fastball ended up in the right-field stands. Perez and the Mets trailed 2-1.

But he didn’t break.

He got ahead of Melky Cabrera and induced a broken-bat groundout, then fanned Robinson Cano to end the inning. No meltdown.

The Mets went ahead on a two-run homer by Endy Chavez in the bottom of the inning.

Mr. Perez’s command didn’t return after that, at least not to the levels he’s achieved in most of his other starts.

He still threw first-pitch balls to 6 of the 13 batters he faced the rest of the way. But ball two did not often follow ball one, and none of the hitters he saw after the first inning reached ball four.

He didn’t overthrow in the sixth when Derek Jeter led off with a single, and Mr. Perez confronted Alex Rodriguez as the go-ahead run. Instead, Mr. Perez trusted his stuff, and sent A-Rod back to the dugout as a strikeout victim.

He got ahead of Johnny Damon 0-2 in the eighth inning; Mr. Damon battled back to 2-2, and on his 108^th pitch, Mr. Perez struck out the Yankees’ leadoff hitter. He then exited to a standing ovation by an ecstatic, gigantic crowd at Shea.

Oliver Perez had managed to defeat, if not dominate, a lineup stacked with offensive stars. He did it on a night when his best command was elusive, and his fastball was less explosive than usual. But baseball’s truly elite pitchers don’t excel only when their pitches are otherworldly. They manage to keep their teams in games even on their off-nights. On Friday night, Oliver Perez finally showed himself capable of doing just that, with a sellout crowd and seemingly all of New York watching.

“Every game is going to be different, in terms of my stuff,” he said after it was over. “Today I was a little bit behind in the count. I just had to keep going and make the next pitch.”

His final numbers do not jump off the page—five strikeouts and two walks in 7 2/3 innings. But Friday night brought Oliver Perez closer to the day that his starts are the ones that the Mets and their fans look forward to.