Gino Gradkowski and A.Q. Shipley have become the center of attention on the Baltimore Ravens' offensive line.

Both players are locked in a competition to replace center Matt Birk, who retired after the Ravens won the Super Bowl in February. Birk never missed a start during his four years with Baltimore, and now it's time for someone else to snap the ball to quarterback Joe Flacco.

At this point, neither Gradkowski nor Shipley has established himself as the favorite to start the opener on Sept. 5 in Denver.

"Everybody says, 'Who's the guy?'" run game coordinator Juan Castillo said Tuesday. "We've got to have some separation. Somebody's got to come to the top. The problem is that they're both playing real well right now. They're both good leaders, they're both tough and ready to fight."

Gradkowski was Birk's backup as a rookie last season. A fourth-round selection out of Delaware, the 6-foot-3, 300-pound Gradkowski saw limited action in 2012 but has the advantage of knowing the system.

The 6-1, 309-pound Shipley came to the Ravens in May via a trade with Indianapolis, where he started in five games last year.

So, what's more valuable — familiarity with the playbook or starting experience?

"I don't know if anyone has the advantage," Gradkowski said. "We're both working pretty hard and both have the system down really well. Obviously game experience helps, but I had some game experience last year, too. I think it's a good battle."

Shipley said: "Anytime you go up against (Green Bay nose guard) B.J. Raji, you've got to get something out of it. I went up against him and a lot of good defensive players in this league. But in terms of me coming here, I felt like a rookie. The terminology is completely different. Once I got it down, though, football is football."

Gradkowski started against Tampa Bay in the preseason opener last week has been working with the first team in practice, but that doesn't necessarily mean he's got the edge. Castillo says Shipley will start on Thursday night against Atlanta.

"The games are very important," Castillo said. "Probably the third game we'll split them up and then make a decision."

This is not a heated competition. Both expect to receive playing time and each is focused on doing his part to get the Ravens back into the Super Bowl.

"We both obviously want the job. Otherwise we wouldn't be here," Shipley said. "That's the only reason to do this thing. But at the same time, we're teammates playing the same position. If a certain scenario comes up on the field, we'll pick each other's brains about it."

Shipley, 27, was a practice squad player during his first two years in the NFL and sat out the 2011 season after being cut by Philadelphia after training camp. But he played in 14 games for the Colts last year and did a fine job negating Raji while Andrew Luck threw for 362 yards and two touchdowns.

Before being traded to Baltimore, however, Shipley found himself hopelessly stuck behind Samson Satele on the Indianapolis depth chart.

"If I would have stayed in Indy I would have had to wait for an injury to get my chance because they were paying the other guy a lot more money," Shipley said. "Coming here, it gives me an opportunity to start, and that's all I ask for."

The final decision is at least two weeks away.

"Those guys are both playing very well, and that's a good thing for the Ravens," coach John Harbaugh said. "We'll just have to see how it all plays out in the next couple of weeks as far as who earns the starting spot."

If Gradkowski wins out, that will give the Ravens a quarterback-center combination from the University of Delaware.

"It's cool for the university," Gradkowski said, "but we didn't play together. It's just a weird coincidence."

In other news, veteran tight end Dallas Clark joined the team after signing a one-year contract. He practiced for the first time Tuesday.

Clark was signed after tight end Dennis Pitta dislocated and fractured his right hip early in training camp and backup Ed Dickson hurt his hamstring. Although it's unlikely Pitta will play this year, the Ravens do not consider putting him on injured reserve to be a formality.

"We'll put him on IR when we're certain he's out for the year," Harbaugh said. "We know it's a serious injury. But when it came back that there was no ligament or cartilage damage, that maybe gave us some hope. So we're going to wait and see how that bone heals."



AP NFL website: www.pro32.ap.org