ANN ARBOR, Mich. -- Jim Harbaugh thinks Michigan's offense must get "more well-oiled" after a shaky performance against Army that nearly brought the season to a grinding halt.

The seventh-ranked Wolverines prevailed 24-21 in two overtimes over Army, a 23-point underdog, but scored just 14 points in regulation, committed three first-half fumbles and had six penalties. They averaged only 2.4 yards per rush against a smaller but active Black Knights defense, which stopped Michigan in several short-yardage situations and forced quarterback Shea Patterson into several mistakes.

"We have to keep grinding, just getting it more well-oiled," Harbaugh said. "We've got to get the well-oiled machine going."

Michigan installed a new offense this year under coordinator Josh Gattis, a first-time playcaller brought in to create more big-play opportunities with the run-pass option and other spread elements. The Wolverines had six different players record a reception of 15 yards or longer against Army, and freshman Zach Charbonnet rushed for 100 yards and three touchdowns, but drives repeatedly stalled because of turnovers, penalties and negative-yardage plays.

"We had some mistakes, we had some penalties, turnovers, things we need to clean up," senior offensive lineman Ben Bredeson said. "It's hard to get into an offensive rhythm with that, but I really like that the team fought through to the end of the game, through all those mistakes, to be able to close it out."

Patterson fumbled on Michigan's first possession for the second consecutive game. He fumbled two series later after a blindside hit by Army's Elijah Riley. Sophomore running back Ben VanSumeren also fumbled in the second quarter.

Michigan has seven fumbles, including five lost fumbles, through the first two games. The Wolverines had only three lost fumbles the entire 2018 season.

"You can't get that loose with the ball," Harbaugh said. "The first one was [Patterson's], and the second one was a missed protection with the running back."

Bredeson said mental focus is the biggest area for Michigan to improve as it enters an open week before visiting Wisconsin on Sept. 21. Wide receiver Ronnie Bell, who led Michigan with seven receptions for 81 yards, said the offense never found a rhythm against Army but grew from handling adversity in the game.

"We've been able to run this system for one spring ball, one camp and now two games," Bredeson said. "I'm liking where we're at, and we're still learning and we're still working some kinks out, too."