Jon Lester Ready to Take Over as Red Sox Ace in 2010 When the 2009 season opened for the Red Sox on April 7, Josh Beckett was the opening day starter. When the postseason started for the Red Sox on Oct. 8, Jon Lester was the Game 1 starter.

The landscape of the 2009 Red Sox vastly changed over the team's six-month season, and that includes who the Red Sox ace is.

The debate between Josh Beckett and Jon Lester at the top of the rotation will continue throughout the winter and into spring training, but Terry Francona made it clear who he believes is the best arm on the Red Sox when he announced his 2009 postseason rotation: Jon Lester.

Outside of the Northeast and AL East, Lester's numbers over the past two seasons have gone unheralded with all the talk focusing on Roy Halladay, Tim Lincecum, CC Sabathia,  Johan Santana, Zack Greinke and Cliff Lee. But there is no reason why Lester shouldn't be in the same conversation with the game's biggest names, since he has become one.

Since his return from his battle with cancer, Lester has posted a 35-14 record with a 3.47 ERA. And last season, Lester averaged 10.0 strikeouts per nine innings and accumulated 225 K's in 203 1/3 innings pitched.

A 25-year-old left-hander in Fenway Park would usually be frowned upon, but Lester has been more than an exception to the rule, posting an 18-4 record and ERAs of 2.49 (2008) and 2.86 (2009) in 31 starts in hitter-friendly Fenway.

And while Lester's career has taken off over the last two years with his breakout season in 2008, Beckett's career has been marred by frustration and inconsistencies.

In 2006, Beckett was far from the ace the Red Sox thought they had acquired from the Marlins, going 16-11 with a 5.01 ERA. He bounced back with a 20-7 record and 3.27 ERA in 2007, including a remarkable postseason and second-place finish in the Cy Young voting. But in 2008, Beckett fell off again (12-10, 4.03) and made his lowest start total (27) since 2004.

This past season, Beckett began the season slow before catching fire in the summer and turning the Cy Young race into a three-man competition with Halladay and Greinke.

On Aug. 12, Beckett was 14-4 with a 3.10 ERA before making just three quality starts over his final nine outings.

In Beckett's only postseason appearance this fall, he allowed four earned runs over 6 2/3 innings, doing nothing to erase his disastrous 8.81 ERA over his three starts in the 2008 playoffs.

As Lester's career has blossomed over the past two seasons, Beckett's continues to take one step forward, two steps back. It has gotten to the point where the Red Sox' best chance to win a game is when Lester is on the mound and not Beckett.

While Lester is under team control through 2013, with a club option for 2014, Beckett only has a club option for the 2010 season. Though the Red Sox and Beckett could work out a new deal, Lester will be the ace of the team next season and in future seasons.

Just seven months ago, Josh Beckett was the Red Sox' No. 1 arm, and Jon Lester was arguably the best No. 2 in the game.

Now Lester is the clear-cut choice to be the No. 1, and Beckett will make a great 1A or No. 2, however you choose to classify him.

A lot changed over one summer, but one thing will remain constant for at least four more years: Jon Lester is the ace of the Red Sox.

NESN.com will be answering one Red Sox question every day in November.

Friday, Nov. 6: What will Jason Varitek's role be in 2010?

Sunday, Nov. 8: Can Manny Delcarmen ever be trusted again?