There’s nothing plain about Prescott’s debut

Da k Prescott shrugs at the suggestion that the Dallas rookie quarterback’s startling success in two preseason games is a product of what skeptics might call the “vanilla” defenses of the exhibition season.

“That’s on them if they want to throw ‘vanilla’ or whatever they want to throw at me, ‘Rocky Road,’ or whatever you want to say,” the 23-year-old former Mississippi State standout said. “I just go out there and just try to concentrate on our game plan and go put out my best.”

Prescott has a preseason NFL-high 158.3 passer rat- ing with four touchdowns, no interceptions and a pair of rushing TDs, giving the Cowboys plenty to think about for a backup to Tony Romo after incumbent Kellen Moore broke his right ankle early in training camp.

Executive vice president of personnel Stephen Jones said the day after Moore’s injury that the Cowboys wanted a veteran in the room with Romo.

The No. 3 quarterback is second-year player Jameill Showers, who spent most of last season on the practice squad.

Jones stops short of indicating he might have changed his mind. But his dad, owner and general manager Jerry Jones, sounds ready to commit to Prescott.

“You would have to say that the more reps these young guys are getting then the better it is for the team, the better it is for their evaluation or their progression,” Jerry Jones said after Prescott threw for two touchdowns and ran for two more in a 41-14 preseason win over Miami.

“If you weigh all of that, the logic goes toward you’re in better shape today to go with them than you were three weeks ago. And I would say we are.”

Prescott likely gets his best test yet Thursday night at Seattle, where he figures to play most, if not all, of the second half. Romo should get the bulk of the first half in what will be his longest preseason outing.

The backup job in Dallas is an important topic because Romo missed 12 games last season with a twice-broken left collarbone. The Cowboys went 1-11 without the 36-year-old during a first-to-worst 4-12 season in the NFC East.

Dallas declined to bring in another veteran to supplant Moore, suggesting he showed enough in two-plus games last season to be a viable backup.

After Moore’s injury, Prescott showed the same qualities the Cowboys say they saw the moment he arrived as a fourth-round pick, the first quarterback drafted by Dallas since 2009.