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INDIANAPOLIS, Ind. – This was what the Indianapolis Colts envisioned when they selected an electric, big-play running back out of South Florida in the fourth round of the April draft.

Explosion from Marlon Mack. Excitement. Big plays in what has been a plodding ground game.

“This is definitely what I try to do, go out there and perform,’’ Mack said after doing precisely that in the Colts’ 26-23 overtime win over San Francisco Sunday at Lucas Oil Stadium.

He led the team with 91 yards and one touchdown on nine carries. Those are elite numbers, but the manner with which Mack amassed them is what’s noteworthy: a 35-yard run, a 22-yard touchdown and a 16-yarder that was oh-to-close to being a 17-yard TD.

Three-time Pro Bowl wideout T.Y. Hilton overcame an early drop and offered his usual big-play expertise to the passing game. He finished with seven receptions and 177 yards, the third-highest total of his career.

Mack offered complementary pop on the ground.

“He brings another dimension to the game: fast, athletic, speed, get around the corner,’’ Hilton said. “Tough guy, man. Tough to bring down.’’

What’s evident is Mack will test the veracity of a defense’s perimeter. He has the suddenness and speed to bounce a play designed to go between the tackles outside and do serious damage.

On his 22-yard touchdown in the third quarter, Mack started up the middle, saw light to his right, eluded defensive lineman Arik Armstead in the backfield, found a seam and outran the 49ers secondary.

On the Colts ensuing possession, it appeared Mack had again found the end zone on a third-and-15 at the 49ers 17. An off-tackle play was bottled up, so he cut to his right, got the corner and sped up the right sideline. Mack dove for the goal line and initially was rewarded with a TD call on the field. Replay disagreed, putting him down at the 1. Jacoby Brissett finished the drive two plays later.

In overtime, Mack helped position the Colts for Adam Vinatieri’s game-winning 51-yard field goal with a 35-yard scamper around right end to the San Francisco 34-yard line.

“He brings (something) different to the backfield,’’ veteran running back Frank Gore said. “He’s got a lot of speed.’’

The only thing that’s held Mack back has been a shoulder injury that kept him out of the last two games.

“We’ve all seen snapshots and glimpses of what he can do,’’ Chuck Pagano said. “He just hasn’t been available all the time. He’s been nicked up.

“It’s great to have him back. That third-and-long in the red zone . . . that play was broken, reversed and circled the defense. It was an unbelievable football play.’’

That type of big-play talent has been missing.

In three games, Mack has had three runs that have gained at least 20 yards: the two against the 49ers and a 24-yarder against the Rams.

Last year, the Colts had only four 20-plus runs all season, and three were by quarterback Andrew Luck.

  • Hilton ‘re-focused:’ Hilton’s monster game – seven catches, 177 yards – started inauspiciously. In the first quarter, he dropped what would have been a 40- or 50-yard completion from Brissett.

“Feels good,’’ he said of the 177 yards and the victory, “but I got a C-minus today. Dropped the one early, but it kind of got me going. Got me refocused.

“I should have caught it, but at the end of the day we got the win and I was able to get a couple of other big plays.’’

Hilton’s contributions included receptions that gained 63, 46, 26 yards and 16 yards.

It marked the 26th 100-yard game of Hilton’s career.

  • Brissett shoulders blame: The Colts nearly suffered a fatal blow in overtime after reaching a first-and-goal at the 49ers 8-yard line. Brissett’s pass intended for right end Darrell Daniels was intercepted at the goal line by linebacker Ray-Ray Armstrong.

“The play was there,’’ Brissett insisted, “and I made a bad throw, one that I know I want back.

“I’ve got to get better at those situations, in critical situations.’’

In the week 2 loss to Arizona, the Cardinals won 16-13 after intercepting Brissett’s first pass in overtime.

Sunday, he had to be calmed down on the sideline by quarterbacks coach Brian Schottenheimer.

“As you could see, I was pretty pissed, but we just moved on to the next play,’’ he said. “The defense did a heck of a job coming up with a big stop there. We definitely needed that.’’

After the defense halted San Francisco’s ensuing drive, Brissett and the offense got into position for Vinatieri’s game-winning field goal.

Brissett completed 22-of-34 passes for a career-high 314 yards.

  • Medical update: Rookie wide receiver and Marian University product Krishawn Hogan had to be helped off the field in the midway through the third quarter after injuring his left knee. He did not return and Pagano said Hogan will undergo an MRI Monday to determine the severity of the injury.

Linebacker Anthony Walker was forced from the game in the second half with a hamstring injury and didn’t return. He missed the previous three games with a hamstring injury.

  • This and that: Gore finished with 48 yards on 14 carries and moved past Eric Dickerson (13,259 yards) into the No. 7 slot in the NFL’s career rushing list. He now has 13,304 and needs 359 yards to pass Jerome Bettis for 6th all-time. . . . Linebacker Jabaal Sheard posted 1.5 sacks and seven tackles. . . . The 49ers remained winless and have lost their last four games by a total of 11 points.

You can follow Mike Chappell on Twitter at @mchappell51.