There weren't any "wow" plays from rookie linebacker Khalil Mack on Sunday, the first day players wore pads, but he is drawing some pretty good comparisons from important training-camp observers.

"He's reminded me of Clay Matthews from Day 1," Oakland general manager Reggie McKenzie said. "He's one of those guys that knows how to set the edge, and he has length and power and some tools to rush the passer.

"He's got that first step, he can bend, he's relentless."

It's that last word that has McKenzie excited about Mack, the No. 5 overall pick, in the same way that he was about Matthews when the Packers drafted him in 2009 (McKenzie was Green Bay's director of player personnel.)

"That's what Clay was, you don't have tell him to go sic 'em," McKenzie said. "He just innately does that. Khalil is that same way."

The comparison is good almost to the pound - Matthews, a four-time Pro Bowler, is 6-foot-3, 255 pounds and Mack is 6-3, 252. But again, it was the heart and not the measurables that McKenzie noticed first.

"It's hard to find guys that are skillful that have that innate ability," he said.