DETROIT -– The 49ers’ new-look run game keyed what classifies as an offensive explosion in the first half Sunday against the Detroit Lions.

But that’s where things ended for the 49ers in in their 32-17 loss at Ford Field. The run game was held to minus-1 yard rushing on three second-half rushing attempts.

“It was a tale of two halves,” 49ers quarterback Blaine Gabbert said.

The 49ers were held without a first-quarter touchdown in the first 14 games. That dubious streak ended on Sunday. The 49ers rolled up 265 total yards in the first half, but managed just 57 total yards after the intermission.

“We started fast and put some points on the board and had a good first half,” Gabbert said. “And we have to find a way to come out and execute better in the second half. It’s plain and simple. We’ve been starting slow and finishing strong, and it was just the opposite today. We have to find a way to put a complete game together and execute at a higher level.”

[MAIOCCO: Instant Replay: Flat in second half, 49ers blow chance vs Lions]

The 49ers got many of their rushing yards out of personnel packages that included three wide receivers. Newly signed running back DuJuan Harris had 74 yards rushing on nine first-half attempts. He had just two rushes for minus-1 yard in the second half.

The 49ers opened the game with an 11-play, 80-yard touchdown drive, capped by Gabbert’s 1-yard scoring pass to tight end Vance McDonald.

 

“(On) the first drive, we had a good tempo and we were running the ball with success,” 49ers Pro Bowl left tackle Joe Staley said. “Just everything we wanted to do was there."

Staley said the Lions made the adjustment to bring safety closer to the line of scrimmage.

“They were doing some stuff that we were anticipating,” Staley said. “We were ready for it. We just didn’t take advantage.”

The 49ers held the ball for less than 7 ½ minutes in the second half. They managed one first down on each of their four possessions in the second half after achieving 16 first downs in the first half.

“I thought we’d come back out in the second half and the second half would be the same thing,” said wide receiver Anquan Boldin, who has five catches for 27 yards in the first half before getting shut out in the second half. “We moved the ball well in the first half. Second half, I don’t know. I don’t know what happened.”

The 49ers punted twice in the second half and their other two possessions ended with failed fourth-down plays, including Jarryd Hayne’s 2-yard pass reception on a fourth-and-3 play.

“Jarryd has got to get to the sticks,” 49ers coach Jim Tomsula said. “Jarryd has to run that route to the sticks. It’s just what has to happen.”

The 49ers might have known what adjustments the Lions were going to make, but they had no answers to get the offense back on track.

“Obviously, they were a step ahead,” Tomsula said. “We weren’t getting things done the way we needed to. A couple key plays in the run game we didn’t get done, and in the passing game we’ve got to be able to get the protection and make a play on the ball.”