The regular season isn’t over, but the Cubs, who boast a 16-game lead in the National League Central, can already turn their attention to the playoffs. Yesterday, I wrote about the two candidates to be Chicago's fourth starter in the postseason. The decision at the opposite end of the rotation is even more intriguing. When the Cubs open the National League Division Series at Wrigley Field on Oct. 7, who will be on the mound?

This would have seemed a silly question at the start of the season. Jake Arrieta was the clear ace of the staff after putting together one of the most dominant second halves in MLB history and winning the NL Cy Young Award in 2015. But while he has been great this season, he hasn't been the almost unhittable pitcher he was last year. Jon Lester has been every bit as good as Arrieta in 2016—their stats are nearly identical across the board—and he has the edge in postseason experience. Neither, meanwhile, has been the most valuable pitcher in the rotation this season. Kyle Hendricks leads all Cubs pitchers with 4.3 Wins Above Replacement (baseball-reference.com version) and sports an MLB-best 2.07 ERA. It’s easy to see why manager Joe Maddon and pitching coach Chris Bosio have a tough decision ahead of them.

This is a problem most teams would love to have, but that doesn’t make coming up with an answer any easier. Remember, too, that being the No. 1 starter in the postseason goes beyond that first game. Whoever starts Game 1 would be in line to start a potential, decisive Game 5 in the NLDS and would likely get the first crack at Game 1 in the NLCS, should the Cubs advance and the schedule allow. With the Nationals and Dodgers in good shape to finish first in the NL East and West, respectively, Chicago's Division Series opponent will be the wild-card team that emerges from a pack that is mostly down to the Cardinals, Giants and Mets. Below is a breakdown of the candidacies for Arrieta, Lester and Hendricks, as well as our pick.