The left-hander took another step toward achieving that goal when he worked seven scoreless innings and allowed only four hits to lead Boston to a 6-0 victory over the Toronto Blue Jays on Sunday at Fenway Park.
Lester improved to 18-8 with a 3.06 ERA this season, and it's still possible Lester could reach the 20-win plateau. But he says he's not concerned about it. If you ask him, this season is not about personal goals.
"Obviously it would be nice, but we've got a long ways to go," Lester said. "I'll just worry about the next one and that's what I've been trying to do here lately."
Red Sox catcher Victor Martinez recognizes how difficult reaching 20 wins could be for Lester.
"This game is tough enough to put any kind of pressure on yourself," Martinez said. "It doesn't change anything if he wins 20 games. If he wins 20 games and we make the playoffs, let's go for it, but it's not going to make any difference. Honestly, it's a great goal for a pitcher to win 20 games."
Since the Red Sox are quickly approaching the end of the regular season and a postseason berth is highly unlikely, Lester's performance this season will stand out as one of the positive aspects of a trying season for Boston.
"In baseball, the round numbers hold some significance," said Red Sox manager Terry Francona. "If you really think about it, what's the difference between hitting .299 and .300? But it looks huge, and 20 wins is kind of that plateau, but [if he doesn't achieve it] it wouldn't take away from what he's done."
There's no doubt Lester has been the ace of Boston's staff for the past couple of seasons, and he's only getting better.
"This kid has gone out and pitched so well. It doesn't matter if it's 17, 18, 19 or 20 [wins]," Francona said. "This kid is phenomenal. In this day and age, he'll hit 20. He may go past it."
There's an old black-and-white picture hanging on the wall in the hallway outside the press box on the fifth floor at Fenway Park.
In the middle of the photo from 1956 is a smiling Mel Parnell. The Red Sox left-hander is holding a baseball and is surrounded by catcher Sammy White and manager Mike Higgins. The photo was taken in the clubhouse on July 14 after Parnell tossed a no-hitter against the Chicago White Sox.
Like Parnell, Lester has thrown a no-no for the Red Sox, his coming on May 19, 2008, against the Kansas City Royals.
If Lester is able to reach 20 wins, he'll become the first Red Sox left-hander since Parnell (1953) to achieve that mark.
With Lester's victory on Sunday, he extended his single-season career high, and his 18 wins ties Bruce Hurst (1988) for the most by a Red Sox left-hander since Parnell's mark in 1953.
On Sunday, Lester got into bases-loaded jams in the third and fifth innings, but both times he was able to stifle Toronto's attack, ending each threat by retiring slugger Jose Bautista.
"He threw the ball pretty good," Martinez said. "He got into a couple of jams, but he was able to make his pitch and get out of it."
Lester never gave in.
"That shows you what kind of pitcher he is," Martinez said. "He goes out there and gives us a chance to win ballgames. It's not fun to face him. I faced him before, and believe me, it's way more fun to be behind the plate."
Francona said Lester was able to stay focused, especially in those tight situations, while working his way out of them.
"He put up a bunch of zeros," Francona said. "His stuff maybe wasn't as explosive as we've seen. He got himself into a couple of situations where he walked a few guys to get to Bautista, but he really made some good pitches. It's not a good feeling when he comes up with men on -- it happened twice -- but [Lester] made good pitches. He stayed in charge of the game."
Lester has been in charge for the majority of the season and that's why he has a chance to reach an impressive milestone.
Joe McDonald covers the Red Sox and the Bruins for ESPNBoston.com.