FRISCO, Texas -- Each week the book on Dak Prescott grows by a page or two. There is more evidence of the Dallas Cowboys quarterback's tendencies, his likes and dislikes, what he does best, what he doesn’t do quite as well.

It's like a baseball pitcher going through the lineup once; true success, however, is measured in how you play when teams know what you are going to do.

Prescott’s start with the Cowboys has been phenomenal. Dallas is 5-1 and in first place in the NFC East. A year ago, the Cowboys won one game without an injured Tony Romo. Through six games they have eclipsed last season's win total.

Prescott has seven touchdown passes and just one interception. The rookie set an NFL record for most passes to start a career without an interception (176). He leads the NFL in Total QBR at 82.9. He has the fifth-best passer rating.

After six starts, the surprise is over.

“I’ve got to stay ahead [of the defense] regardless, no matter what number of games this is in my season or in my career,” Prescott said. “That’s what’s gotten me to this level: It’s preparing, watching the defenses, and that’s what I’ll continue to do.”

In 2006, Romo went 5-1 in his first six starts, propelling the Cowboys to a playoff spot. He threw 10 touchdown passes and was intercepted just four times. In his next four starts, the Cowboys went 1-3 and Romo had six touchdowns with six interceptions.

In Romo’s first six starts, he faced one defense that finished the season in the top 10 in yards and points -- the Carolina Panthers, in his first start. In his final four, he faced two defenses that finished in the top half of the league in yards and three in the top half in points allowed.

So far this season, Prescott has faced one top-10 defense in yards (the Green Bay Packers) and one top-10 defense in points (the New York Giants). The Philadelphia Eagles, Sunday’s foe, have the fifth-ranked defense in yards and have allowed the third-fewest points.

In their final 10 games, the Cowboys have four games against defenses in the top 10 in yards and five in the top 10 in points allowed.

As the level of competition grows, the more Prescott will have to handle. He said there have been only a couple of looks that have surprised him during the first six games.

“Every team kind of has their one play or their one blitz they’re going to bring on third down that they haven’t done at all this year,” Prescott said. “But just because it’s their first time I have seen them do it, [that] another team has done it kind of gives me answers.”

The Cowboys’ best answers have involved their running game. Ezekiel Elliott's success has kept pressure off Prescott. He has not had to pass Dallas to a victory. But in his past two games, he has three turnovers: two fumbles, one interception.

Eagles rookie quarterback Carson Wentz also is seeing the book on him grow. He is coming off his first two-interception game, against the Minnesota Vikings. He has three interceptions in his past three games. He has fumbled six times but lost just one.

Staying power matters as a quarterback. In 2012, Robert Griffin III so petrified Jerry Jones that the Cowboys owner and general manager thought the Washington Redskins were about to run the NFC East for years to come. In 2013, Nick Foles had 27 touchdown passes and two interceptions for the Eagles, but he was traded two years later and is now on his third team in three seasons as a backup with the Kansas City Chiefs.

Romo proved to have staying power. In 2007, he led the Cowboys to a 13-3 record and threw a career-high 36 touchdown passes.

Prescott now has to show he has staying power. Same with Wentz.

“If you’re winning games, you’re doing it for a reason, and I don’t think you have to change the formula to winning,” Philadelphia coach Doug Pederson said. “I think, No. 1, you’ve got to stay healthy. Your offensive line has got to be healthy. The ability to run the football obviously is a great formula to the success of these quarterbacks. I think one, especially in Dak’s case, is just not turning the ball over. Even Carson, not really forcing or turning the ball over as much. Playing smart.

"Sure, teams are going to have more information. They’re going to have a bigger picture here after a few more games on these quarterbacks, but the formula doesn’t have to change. ... Are they going to go win a game somewhere? Sure. That’s without saying. But at the same time, you don’t have to put everything on their shoulders, especially early in their careers.”