FRISCO, Texas (AP) Tyron Smith and Travis Frederick signed lucrative second contracts with Dallas after starting right away as first-round picks, and Zack Martin is next.

The Cowboys have made significant investments in their offensive line for five years, and it's paying off for two rookies and budding stars in quarterback Dak Prescott and running back Ezekiel Elliott.

Dallas doesn't even miss the injured franchise leader in passing yards and touchdowns, Tony Romo. And opposing defenses are certainly noticing.

''Now I see why he's got 100 million dollars on his line,'' Cincinnati cornerback Adam Jones said after last week's 28-14 loss to his former team and former boss, Dallas owner Jerry Jones. ''Some of those holes my daughter could have run through.''

The Cowboys (4-1), who visit Green Bay (3-1) on Sunday, hadn't drafted a lineman in the first round since Jones bought the team in 1989 when they took Smith ninth overall in 2011 thinking he would eventually be their left tackle.

Two years later, Frederick went 31st, then Martin at No. 16 the year after that.

Three first-rounders in four years, followed by an eight-year, $98 million extension for Smith that pushed the total value of his deal over $100 million and made him the second player after Romo in franchise history to hit that mark.

This preseason, Frederick signed a six-year, $56 million extension that makes him the highest-paid center in the NFL.

Martin figures to get something in the range of $10 million per season - tops among the league's right guards at the moment. And it's at the bottom of his list of concerns.

''We focus on what's important,'' Martin said. ''It's not hard to stay on the straight and narrow in that room.''

Doug Free, a 32-year-old right tackle in his 10th season, has been the other constant on the line the past five years.

Ron Leary, undrafted four years ago, started at left guard for two years before the addition of La'el Collins, a projected first-rounder who went undrafted last year because his name surfaced in a murder investigation just before the draft. Collins replaced Leary last year, but Leary is starting again with Collins sidelined by a toe injury.

Frederick credits former Dallas center Phil Costa because he says Costa knew the job was going to Frederick and his teammate ''still taught me everything that he knew.'' Martin says he was just following the example of fellow first-rounders Smith and Frederick.

And Frederick said Leary and Collins worked through a potentially awkward situation with both staying on the roster after Collins took over. Leary asked for a trade that never came in the offseason, but was ready when Collins went down.

With Leary starting again, it's the same line that blocked for NFL rushing champion DeMarco Murray in 2014. Now Elliott is the league leader with 546 yards through five games.

''I think the common denominator is the group,'' Frederick said. ''The group helped bring me along the right way. It would have been really easy for those guys to say, `Oh, he's a rookie, we're not going to help him out.'''

While Elliott struggled with a per-carry average of less than 3 yards in an opening loss to the New York Giants, the average has risen steadily since. The former Ohio State star had his first breakaway touchdown against the Bengals, a 60-yarder that put Dallas up 28-0.

Prescott has been sacked seven times, matching the second-lowest total in the league. The protection probably has something to do with him being eight passes away from breaking Tom Brady's record of 162 attempts without an interception to start a career.

Tight end Jason Witten, in his 14th season, says Frederick's intelligence helped him master Dallas' system quickly, and Martin's athletic ability helped him transition to guard after spending significant time at tackle at Notre Dame.

''And of course Tyron,'' Witten said. ''If you can pick one guy, that's who you're picking.''

And Smith started a trend that's paying off for the Cowboys.

''O-linemen, we kind of put them in this box,'' Witten said. ''But when you have success, it can get to anybody. That group, if anything they put their head down even more and go to work.''



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