2012 has been a season to forget for Jon Lester. (AP)

To put it bluntly, 2012 has been a season to forget so far for Jon Lester. The 28-year-old does not pretend otherwise.

“It’s a [expletive] first half for me,” he rued after entering the All-Star break with one of his worst outings of the season.

The Red Sox left-hander’s woes have been just one ingredient in the recipe of the team’s beleaguered pitching staff, but they might be the most significant. The two-time All-Star and former Cy Young candidate is on track to have the worst statistical season of his career during a time in which his team can’t afford such struggles.

It’s no secret that the Red Sox have been marred by inconsistency this season — mostly due to the array of players that has and still is occupying the disabled list — and the pitching rotation has taken a large brunt of the damage.

With Josh Beckett battling injuries and controversy this season, Clay Buchholz suffering a recent gastrointestinal malady that landed him on the DL and a combination of demotions, minor league promotions and bullpen shuffling, the Sox have had little room for error, especially from a pitcher of Lester’s experience and ability. Lester, along with fellow starter Felix Doubront, has been the only consistently healthy arm this season.

But while Doubront has put together a surprisingly impressive season, it’s been Lester who has put together a campaign that has been equally surprising for its inconsistency. Sunday night’s 7-3 loss to the Yankees represented another page in this half-season chapter of struggles: nine hits surrendered, five runs (four earned) allowed, two walks, one hit batter and 101 pitches in only 4 1/3 innings.

“Jon had another uphill battle,” Red Sox manager Bobby Valentine said. “I thought he was throwing the ball well, but before you know it, you look up and there’s a lot of hits on the board and runs and base runners and pitches. One hundred pitches and we’re not through the fifth inning yet, it’s not what he wanted I’m sure.”

Lester’s pitch count climbed quickly thanks to yet another ineffective first inning in this series by Red Sox starters. Lester gave up back-to-back singles to Derek Jeter and Curtis Granderson to start the game and then Mark Teixeira brought Jeter home with an RBI double. After Robinson Cano walked and Nick Swisher added another RBI on a fielder’s choice, the Yankees were already up 2-0 before the Red Sox came to bat.

Lester had seemed to settle down beginning in the third, retiring the last two batters in a row to end the frame before striking out the side in the fourth. But the fifth inning ultimately spelled the demise of the southpaw. Teixeira led off with a single and Alex Rodriguez then drove him home with a triple to the triangle in center. Lester was done after yielding a walk to Cano and an RBI single to Swisher.

“It’s obviously not good. You have to get deeper in the game somehow,” Lester said. “Too many pitches, too many foul balls, too many deep counts. … With a good team like that, you can’t do that.”

Facing the Yankees, the team with the best record in the American League, is one challenge, but it’s been a long list of challenges in 2012 for Lester. After Sunday night’s loss, Lester is 5-6 with a 4.49 ERA, both of which are on track for the worst marks of his career. He’s never had a losing record or struggles of this variety in any one of his previous six seasons.

Looking forward, Lester will receive an extended rest as the Red Sox head into the All-Star break. After a five-day layoff between now and Friday, he’ll wait even longer as he’s not scheduled to pitch again until July 17 in the White Sox series, according to Valentine.

With eight days of rest, it could be the perfect opportunity for Lester to put a forgettable first half behind him and try to get back to his All-Star caliber form.

“[These are] uncharted waters for me,” Lester said. “You just have to keep grinding it out. Can’t give up, just have to keep working. All I can control is showing up every day, working hard and I think things are going to turn around.”