BOSTON -- It all starts up again for Jon Lester on Tuesday night at Fenway, when he takes the ball against the Yankees. The first few chapters of Lester's 2010 season could provide the answer of whether he's ready to make the leap from standout pitcher to American League Cy Young Award candidate.

Without question, he has emerged into one of the top left-handed starters in baseball over the past two seasons. But he stumbled out of the gate in both 2008 and '09. Last year, the slump lasted until May 31, when Lester took the ball in Toronto with a 6.07 ERA. Lester dominated on that Sunday afternoon, and in most of his starts thereafter, finishing the year with a 15-8 record and a 3.41 ERA.

At 26 years old, Lester is at the age where most pitchers start to settle right into their prime years. And for the power lefty, there are a few keys to taking the next step. One, Lester says, is mental. He admits now that he was his own worst enemy in the opening two months of 2009.

"I learned that you can't worry about the ending of a game before it even starts," Lester said. "You have to go out there and take it one pitch at a time, and it sounds stupid and it sounds easy, but a lot of times it's not. You want to go out there and you want to succeed right away, and from the first pitch on, you want to win the game. But you have to take it one pitch and one inning at a time. I wasn't doing that last year at the beginning of the year, and I finally got into a little bit of a rhythm and was able to do that."

Because Lester has done so much already -- from winning that clinching World Series game in 2007 to firing the no-hitter in '08 to pitching the postseason opener the past two seasons -- it's easy to forget that there is still some natural progression that needs to take place.

"He's been working on first-pitch strikes and his changeup," said Red Sox manager Terry Francona. "If you think you can't improve, it's probably going to go the wrong way. He's always hungry to do better. There's still more there, which is good for us."

Sandwiched in between Josh Beckett and John Lackey to make up Boston's big three, Lester is probably the one in the bunch whose ceiling is a bit unknown. Beckett and Lackey have both developed a predictably strong track record that has put both of them in All-Star Games and earned them the ace label throughout the years. If things continue to improve for Lester this year, there's a chance he could emerge into Boston's most dominant starter.

Lester's fastball, cutter and curveball have been certifiable weapons, and if the changeup can become that same thing, he might dominate.

"It gives them something a little slower that comes off my fastball and just makes that stuff a little bit crisper and a little bit better," Lester said. "It's just a different look. Any time you can refine something or add something to what you're doing right now to make you better, it obviously makes you better.

"The changeup is obviously a huge difference in what I've always thrown, and if we can get that into my game a little more often than we have in the past, it just, I think, takes a lot of pressure off my fastball and cutter and, like I say, gives me another weapon to use against tough hitters."

Even if his stuff is explosive, Lester enjoys trying to outthink the hitters.

"I like playing the cat-and-mouse game of what I'm going to throw next and what location, and that's when it becomes fun," Lester said. "When you're able to not worry about, 'Am I going to be able to throw strikes?' or 'Am I going to be able to command the zone?' You're worried about getting a hitter out and how you're going to do it. That makes the game fun, regardless of whether you're winning or losing. That makes pitching, pitching. When you're able to go out there and kind of dictate the tempo of the game, it makes it a lot easier."

It's fairly evident when Lester isn't having his way out there, as he tends to pitch at a more plodding pace. If he is working quickly, it likely means he's in a groove.

"The biggest thing we can do, and we try to pound it home with everybody, is [for him] to get it and work quick," Francona said. "It's the same thing we tell [Clay Buchholz]. Every pitch isn't an event. When you're making effective pitches and you get it and work quick, it sort of has a carryover."

When Lester is in rhythm, his arsenal is a most unpleasant experience for opposing hitters.

"He's special," said catcher Victor Martinez. "He keeps that cutter pretty tight on right-handers. He throws that changeup. As a hitter, I used to face him and you'd just go out there and hope he makes a mistake on you, and [you] had to make sure you didn't miss it. That's what makes him so tough. He can control it from both sides of the plate. And don't forget about that curveball."

There's probably no better test of where Lester is at heading into this season than the opponent he will face. The Yankees are loaded offensively, and as they showed against Beckett on Sunday's Opening Night, they will make pitchers pay dearly for mistakes. The Red Sox went on to win that game, 9-7, and if Lester has his way, they can play from ahead instead of behind in Game 2.

"They're obviously very tough," Lester said. "They're the World Series champs for a reason. I think the thing that is the biggest key with them is they don't give you a lot of breaks. With different lineups, you can sometimes take a mental break and get guys out. And with the Yankees, you can't do that. You have to be on top of your game mentally and physically every pitch and every at-bat. They're not going to give in."

And unlike the past two seasons, Lester hopes there is no give to him in the early going. This time, he will try to start on a roll and stay there.