Jon Lester's 19th start of the year began uneventfully enough: a line drive single to center field, followed by a 6-3 fielder's choice to nab the next batter. Less than an hour later, the lefty was done for the day, failing to get out of the first inning for the first time in his career.

That was the scene on Sunday, when the Chicago Cubs hosted the Pittsburgh Pirates for their final game before the MLB All-Star break. Lester had more than enough opportunities to right the ship, but after 12 batters faced, two home runs and a whopping 10 runs surrendered, the 33-year-old veteran was pulled in favor of fellow southpaw Mike Montgomery.

Montgomery and the other Chicago relievers who took the mound, Dylan Floro and Eddie Butler, weren't nearly as bad, but the damage was already done. The Cubs lost to their division rivals by a score of 14-3, falling to an uninspiring 43-45 on the season.

They now sit 5.5 games adrift of the Milwaukee Brewers in the race for the National League Central. What's more, they're well off of their pace from last year, when they won 107 games in addition to the franchise's first World Series title in 108 years.

With a solid core of young hitters and an experienced rotation, the Cubs appeared to be set up for long term success and were a popular pick to go back-to-back at the start of the season. However, far too many essential players have either underachieved or been injured, and many suggest that fatigue is the culprit.

"It seems to me like they're worn out," said ESPN baseball writer Jerry Crasnick. "You go through what they went through last year...think of all the attention and the pressure and the talk...It just shows it's hard to repeat."

Because of their deep playoff run, several Cubs pitchers were asked to shoulder especially heavy loads last fall. Lester, for example, pitched over 35 postseason innings, giving him a total of 238.1 for the entire year. Perhaps unsurprisingly, he's been a different pitcher this year -- his ERA has ballooned by nearly two full runs, while his home run rate is the highest it's been in a decade.

Look elsewhere in the rotation, and the story is similar. Kyle Hendricks and John Lackey are currently on the disabled list. 2015 Cy Young Award winner Jake Arrieta, like Lester, is having his least effective campaign in years. All have struggled with their velocity this season.

The lineup still features some big pieces -- perennial MVP candidates Kris Bryant and Anthony Rizzo are still hitting -- but the Cubs have had their share of disappointing performances at the plate too. Taking park effects into account, Jason Heyward, Kyle Schwarber, Addison Russell and Ben Zobrist have all been well below average this year, weakening a lineup that used to be one of baseball's deepest.

As if that wasn't bad enough, the Cubs continue to run into patches of bad publicity. Last month, veteran catcher Miguel Montero criticized Arrieta for his slow delivery, resulting in his dismissal from the team. When the All-Star Game rosters were announced last week, the 2016 Cubs became the first World Series winner ever to not have a single player represented in the following season's Midsummer Classic.

But even with all their struggles, there is hope for Chicago. The NL Central is one of MLB's weakest divisions, and besides, manager Joe Maddon hasn't lost faith in his team yet.

"I'm very pleased with where we're at right now," he said over the weekend. "We have gone through a lot of different moments already this season regarding injuries, etc., and we've held our heads up pretty good."