Ball security.

If St. Augustine has had a mantra during the past fortnight, that would be it. Protect the football.

The Purple Knights did just that in playing turnover free while rolling for 171 yards and three touchdowns rushing to soundly defeat Catholic League rival Holy Cross, 34-9, in the first round of the Division I state playoffs on a cold and windy Friday night at Joe Yenni Stadium.

Tenth-seeded St. Augustine (6-5) earned some additional gratification in rebounding from a 24-20 loss to these same Tigers two weeks ago in which the Purple Knights committed three second-half turnovers to squander a 14-3 lead at intermission.

Those roles were reversed this time around as the Tigers committed three second-half miscues — a fumble and two interceptions — while the Purple Knights assumed control of both sides of the line of scrimmage to shake loose from a 7-7 halftime stalemate.

St. Augustine now advances to play No. 2 seed and reigning state champion Catholic of Baton Rouge next Friday in Baton Rouge.

“These past two weeks we’ve been turning the ball over,’’ said St. Augustine quarterback Trevon Woodson after accounting for 141 of his team’s 254 yards with his running and passing. “So our emphasis has been on eliminating our mistakes and limiting the turnovers. I felt like we had them tonight on both sides of the ball.

“We were very physical upfront. The offensive line did a great job. We had great coaching, great play-calling. I don’t know if the game could have been called any better.’’

Seventh-seeded Holy Cross (7-4) completed its first season under Coach Guy LeCompte by being held to minus-3 yards rushing by the Purple Knights' swarming run defense. The Tigers entered the game having won their past two regular-season games and three of the final four.

Holy Cross did manage 158 passing yards by sophomore quarterback John Dade Wooton, but many of those yards came under duress during a 9-of-21 performance that included a pair of interceptions by St. Augustine defensive backs Joshua White and Damon McFarland Jr.

It was a 41-yard interception return for a touchdown by McFarland late in the fourth quarter that punctuated the Knights’ statement.

“No,’’ St. Augustine coach Nathaniel Jones said when asked if revenge played any role. “I just think in the playoffs that it’s win or go home. So you want to make sure you give your best effort. I think we stayed the course. We executed well. We played disciplined and we played by our rules.’’

Freshman running back Justin Doyle rushed for St. Augustine’s first two touchdowns on runs of 10 and 6 yards in the second and third periods and Jaron Marks III kicked the first of four successful PAT kicks to give the Purple Knights a 14-7 early in the third quarter that they would not relinquish.

Woodson then added to the lead with a 20-yard scoring pass to wide receiver Tylie Keasley following a fumble recovery and return by safety Tahj Adams before running back Mahmood Bailey ran 14 yards for the Knights’ final offensive touchdown.

Holy Cross scored its points on a 27-yard scoring pass from John Dade Wooton to wide receiver Jalen Johnson in the second quarter that featured cross-field running by Johnson. The big play converted a third-and-17 situation that Nolan Heitmeier followed with a successful PAT kick with 2.

The Tigers defense accounted for the other points when defensive end Dominic Lamm sacked Woodson for a 16-yard loss in the third quarter.

Bailey paced St. Aug’s running game with 75 yards on 12 attempts followed by Woodson with 58 yards on 15 carries and Doyle with 46 yards on 12 attempts.

“Our kids played hard,’’ Lecompte said. “Congratulations to St. Augustine, their coaching staff and their kids. They played hard as well. They had a good game plan. They changed their game plan up from what they had done most of the season. This thing just kind of snowballed on us at the end. When you get in a situation where you need to throw it, things can snowball on you.’’