The San Francisco 49ers used their first of two third-round picks to add more help on defense.

With the No. 75 overall pick, the 49ers snagged Oklahoma State linebacker Nick Martin, making it three defensive players in three selections.

Martin, 22, played 35 games with 19 starts in four years with the Cowboys. He racked up 203 tackles, 23.5 tackles for loss, seven sacks, four pass breakups and two interceptions.

The 49ers value athleticism in the second level, and Martin brings that in spades. He ran a 4.53 40-yard dash at the NFL combine, but his play speed looks faster than that. He’s a little undersized at 5-11, 221 pounds, but he’s a tenacious run defender with a ton of upside in coverage. Staying on the field for all three downs is going to be crucial for Martin and this pick after LB Dre Greenlaw left in free agency.

Martin joins a revamped 49ers front seven that now features first-round defensive end Mykel Williams and second-round defensive tackle Alfred Collins.

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