Bill Belichick walks the fields during Thursday morning's practice. (John Vu/WEEI.com)

FOXBORO — Under overcast skies with a pretty persistent rain (which yielded toward the end of practice), the Patriots opened the 2010 season with a morning practice on the fields behind Gillette Stadium. In a practice that ran for roughly 90 minutes, almost everyone except linebacker Derrick Burgess and offensive lineman Logan Mankins was present and accounted for.

•Mankins’ absence was explained by Patriots coach Bill Belichick in his press conference, who explained, “All of the players that are here are under contract and Logan is not under contract.” Nick Kaczur appeared to take the majority of snaps in his place at left guard. Dan Connolly also saw some action there as well.

•Wide receivers Sam Aiken and Darnell Jenkins and defensive lineman Ron Brace did not participate in practice, working in the corner of the field by themselves. In addition, wide receiver Wes Welker, working in shorts and a T-shirt, stretched with his teammates at the start of practice, but retired soon after to go through a spirited workout of his own in the corner of the field with Harold Nash and Joe Van Allen of the strength and conditioning staff. Welker did sprints, and worked with a resistance rope. He was out on the field for almost all practice, and appeared to really be working up a sweat. If I had to guess, this is a guy who is coming off PUP sooner rather than later.

•The first day of training camp saw more than its share of penalty laps, many of them run by veterans: Fred Taylor and Vince Wilfork each took a lap, as well as Ryan Wendell and Zac Robinson when the two failed to connect on a snap.

•Spent a lot of this morning’s session keeping an eye on wide receivers — Matthew Slater, who has been all over the field in his brief career in New England, was running with the receivers this morning. In addition, a Tom Brady-to-Taylor Price deep connection near the start of practice drew big cheers from the soggy crowd. But the unquestioned highlight of the day was a Brady-to-Randy Moss pass play that appeared to go for roughly 50 yards. On the play, Moss beat the defense and got behind veteran James Sanders, hauling in the pass before being knocked out at the two-yard line. (Brandon Tate just missed a pass from Brady in red-zone drills.)

•In special teams drills, Tate, Price, Julian Edelman and Devin McCourty worked as kick returners.

•When it came to positional drills, the safety tandem of Brandon Meriweather and Pat Chung were together with the starting defense, while Brandon McGowan and James Sanders were together with the No. 2 defense. At corner, Leigh Bodden and Darius Butler were there with the No. 1 defense. And Jerod Mayo and Gary Guyton were together at the inside linebacker position with the starting defense, while Tyrone McKenzie rotated in.

•For his part, Pierre Woods had a couple of really impressive stops on red-zone work, taking down Laurence Maroney on a pair of sequences at the goal line, drawing cheers from the crowd.