By Bruce Levine–

CHICAGO (CBS) — The fatal first inning has been the Cubs’ Achilles heel so far this season, as their starting pitching has given up 32 runs in the opening frame of the 25 games played.

More than anything else, that has put the defending champion Cubs back on their heels in the early going as they’ve opened 13-12.

On Monday evening, it was left-hander Brett Anderson starting in a rainstorm before it began hailing line drives. Anderson gave up four first-inning runs and three more in the second. Anderson allowed seven earned runs on seven hits in 1 1/3 innings.

This could be his last start for Chicago. The outing raised his ERA from 3.54 to 6.23. The Cubs could never come back, falling 10-2 to the Phillies at Wrigley Field.

Left-hander Mike Montgomery came in as the replacement for Anderson and could get the call as the starter the next time this rotation spot comes up. Mongomery battled Anderson for the fifth rotation spot throughout spring training before he was sent to the bullpen in late March.

Manager Joe Maddon talked about how Anderson hasn’t settled into Cubdom as of yet.

“I am still seeing him as adjusting to being here,” Maddon said pregame. “I don’t know if he has fully landed. As he really settles in, heads up.”

In the case of Monday evening, it was heads up for the Cubs position players, as Anderson was getting shelled with line drives by the Phillies.

The Cubs have averaged 6.8 runs in the team’s 13 victories. In the 12 losses, they’ve averaged three runs. Starting behind the eight ball with all of these blowout first-inning debacles has been a factor in these up-and-down offensive numbers.

Montgomery could be the next move for Maddon after the Anderson debacle.

“Look, we had a horrible night,” Maddon said. “I thought another real positive was Montgomery’s performance. We got him stretched out”

If Montogomery does start in five days, he will have the benefit of having thrown 52 pitches in his longest performance relief outing as a Cub, one in which he threw 3 2/3 scoreless innings.

“To come into a game early like that can definitely be a little challenging,” he said. “I was able to get out of a couple of jams today by making some good pitches. Whatever they decide my role is I just have to go out and get outs. I am ready to do anything as I showed in spring training. You obviously want your teammates to do well. You have to have the mindset that when they call your name you must be ready to answer the bell.”

Anderson has almost no experience as a relief pitcher. The likelihood of him going to the bullpen if Montgomery starts is remote.

Bruce Levine covers the Cubs and White Sox for 670 The Score and Follow him on Twitter @MLBBruceLevine.

Watch & Listen LIVE