MORGANTOWN, W.Va. — Freshman Geno Smith was relaxed and ready when West Virginia quarterback Jarrett Brown went down with an injury.

Smith led the Mountaineers on four scoring drives in the first extensive play of his young career, including throwing a 33-yard touchdown pass, and West Virginia overcame its first halftime deficit of the season to beat Marshall 24-7 Saturday.

‘‘I think he did pretty well,’’ coach Bill Stewart said. ‘‘I thought in my heart he knew where to put the ball.’’

Noel Devine rushed for 103 yards and two touchdowns as West Virginia (5-1) improved to 9-0 against Marshall (4-3) in the series between the state’s only Football Bowl Subdivision teams.

Devine outdueled Marshall’s Darius Marshall in a matchup between two of the nation’s top three rushers, although both players struggled to find running room on a cold and wet afternoon.

Devine was held 23 yards below his third-best average. Marshall, whose 146-yard average ranked second to Fresno State’s Ryan Mathews’s 148, was limited to 82 yards and lost a second-quarter fumble at the West Virginia 8.

With only 313 yards of offense, West Virginia didn’t overwhelm Marshall. With No. 20 Oklahoma, No. 21 South Florida and No. 25 Notre Dame among the ranked teams that lost, the Mountaineers will find out Sunday if they’ll join unranked Pittsburgh and No. 8 Cincinnati in the Top 25. That would give the Big East three ranked teams for the first time this season.

Brown took a helmet-to-helmet hit on West Virginia’s first series and did not return. Stewart said he didn’t know the extent of Brown’s injury. The Mountaineers enter the heart of the Big East schedule starting next Saturday at home against Connecticut.

The 6-foot-3 Smith won the backup job during preseason camp after throwing for 3,089 yards and 32 TDs last season at Miramar (Fla.) High School and saw limited play late in two games earlier this season.

With former WVU standout Pat White watching from the sidelines, Smith completed 15 of 21 passes for 147 yards.

‘‘Coach always tells me to stay ready for these situations,’’ Smith said. ‘‘I’m always comfortable. I was comfortable at the beginning of the game. It was just a matter of me making my looks at the defense and making my reads a little quicker because they (Marshall) were running a lot of different things out there.’’

Smith said offensive coordinator Jeff Mullen’s play calling ‘‘allowed me to get into a rhythm early. And in the second half, we just basically lit them up.’’

After West Virginia was limited to two first downs and 84 yards of offense in the first half, its defense came up big, holding an opponent scoreless after halftime for the second time this season.

West Virginia’s first 17 points came off of Marshall mistakes.

Brandon Hogan, who also had a fumble recovery, intercepted Brian Anderson just before halftime that led to a field goal.

A short punt put West Virginia at the Marshall 46 on its first series of the third quarter. Smith’s 14-yard pass to Jock Sanders on fourth down kept the drive going and Devine finished it with a 14-yard run for a 10-7 lead. Devine would add a 9-yard TD run late in the fourth.

Linebacker Reed Williams stripped the ball from Marshall tight end Cody Slate on the first play of the fourth quarter and J.T. Thomas recovered at the West Virginia 27. Smith took the Mountaineers down the field in five plays, capped by his scoring toss to Alric Arnett in the back of the end zone.

‘‘He was really impressive,’’ Arnett said of Smith. ‘‘You really can’t put it into words. He’s a freshman and came out and played an outstanding game against a good team when we were down with our backs against the wall. It says a lot about his character.’’

Marshall’s Brian Anderson scored on a 12-yard run on third down in the first quarter. He completed 17 of 35 passes for 149 yards and was intercepted twice.

‘‘The key in the locker room at the half was which team from our state was going to come out in the second half and play the second half that we both have been playing,’’ said Marshall coach Mark Snyder. ‘‘It was them.’’

Marshall stats

West Virginia 24, Marshall 7

Marshall 7 0 0 0 — 7

West Virginia 0 3 7 14 — 24

First Quarter

Mar — Brian Anderson 12 run (Craig Ratanamorn kick) 8:14

Second Quarter

WVU — Tyler Bitancurt 32 field goal 1:55

Third Quarter

WVU — Noel Devine 14 run (Tyler Bitancurt kick) 3:00

Fourth Quarter

WVU — Alric Arnett 33 pass from Geno Smith (Tyler Bitancurt kick) 2:20

WVU — Noel Devine (Tyler Bitancurt kick) 4:33

A—54,432

———

Mar WVU

First downs 16 13

Rushes-yards 34-58 31-147

Passing 149 166

Comp-Att-Int 17-35-2 16-23-0

Return Yards 64 98

Punts-Avg. 6-39.0 6-45.2

Fumbles-Lost 6-2 3-2

Penalties-Yards 3-40 5-50

Time of Possession 32:01 27:59

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INDIVIDUAL STATISTICS

RUSHING—Marshall: Darius Marshall 25-82, Kase Whitehead 1-1,Press Taylor 1-0, Brian Anderson 6-minus 12, Team 1-minus 13. West Virginia: Noel Devine 19-103, Geno Smith 6-17, Jarrett Brown 1-15, Coley White 3-7, Jock Sanders 1-3, Mark Rodgers 1-2.

PASSING—Marshall: Brian Anderson 17-35-2 149. West Virginia: Geno Smith 15-21-0 147, Jarrtt Brown 1-2-0 19.

RECEIVING—Marshall: Cody Slate 10-102, Darius Marshall 3-0, Antavious Wilson 2-35, Chuck Walker 1-6, Wayne Bonner 1-6. West Virginia: Jock Sanders 4-39, Alric Arnett 3-55, Wes Lyons 3-53, Brad Starks 3-minus 1, Noel Devine 1-20, Will Johnson 1-5, Tavon Austin 1-minus 5