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FOXBORO - At first glance, the Patriots' defensive unit is almost not recognizable from the start of the season, let alone last year.

Players such as Jonathan Wilhite, Deltha O'Neal, Terrence Wheatley, Brandon Meriweather and Mike Richardson are seeing more and more time on the field in the Patriots' defensive backfield, as are rookie linebackers Jerod Mayo and Gary Guyton in other formations.

It's out of necessity; the season has almost become a war of attrition for the Patriots, but one they seem to be winning.

The Patriots improved to 5-2 Sunday with a 23-16 victory over the St. Louis Rams at Gillette Stadium, a game that was not decided until O'Neal, the ninth-year veteran cornerback from California who joined the team in the waning hours of the preseason, returned from a "head injury" suffered on the game's first series to intercept a Marc Bulger pass at the Patriots' 16 and return it 47 yards with 1:08 left to play.

With Rodney Harrison out for the season with a quadriceps tear, Lewis Sanders inactive for the game and Ellis Hobbs banged up at its finish, the Patriots had to turn to newcomers and rookies to get by against a rapidly improving team. "When guys go down, at lot of things happen," said fourth-year veteran safety James Sanders, now the "dean" of the secondary in terms of service with the Patriots.

"But Bill Belichick is the king of moving people around and putting us in a position to make plays. When guys go down, others step in and we try not to miss a beat.

"And for the most part, we don't," Sanders added.

With a renewed focus on pressuring the quarterback, the Patriots' front seven made things a little easier for the secondary. Richard Seymour had his best start of the season with seven solo tackles and one sack, Ty Warren added a sack and four tackles, Tedy Bruschi registered a game-high 11 tackles and Adalius Thomas sacked Bulger twice for minus-26 yards to go along with his seven tackles.

"It seemed like we had some decent pressure on the quarterback," Belichick said. "I think it could have been better a few times, but we knocked him down, we were in the pocket and made him run out a few times, too. That was good.

"We probably could have done a little better, but in the end, it was enough," Belichick added.

Bulger still completed 18 of 34 passes for 301 yards, but he was sacked four times for 33 yards in losses and just 124 of those passing yards came in the second half.

Knowing that the secondary has endured its share of injuries, Warren said it helped the defensive tackles to stay the course and just focus upon what was needed from them. At the same time, he said, others stepped up their game as well.

"In the fourth quarter, a lot of guys stepped up and came up with some plays that we needed when it was tied up," he said. "The offense did a good job of capitalizing at the right time and our special teams and so forth. I would say so."

So far, Warren said, the onslaught of injuries has not forced wholesale changes to the Patriots' playbook. "You just have to go out there and deal with what you have," Warren said. "Due to some injuries and stuff, it's realistic that maybe some schemes or things like that could change, but hopefully everybody can get out there and get healthy. To have everybody out there, especially going into the Colts' game will be a plus for us."

If anything, the Rams made more adjustments than the Patriots - especially after a second-quarter sequence in which Thomas and Seymour posted sacks within a three-play span, dropping Bulger for losses of 13 and 2 yards respectively and stopping a potential scoring drive at the Patriots' 40.

"They did change their protection and didn't go back to that certain protection again," said Thomas. "So I guess they made some kind of adjustment on the sideline and did something totally different."

Not different enough, as it turned out.

MARK FARINELLA may be reached at 508-236-0315 or via e-mail at mfarinel@thesunchronicle.com. Read Farinella's blog, "Blogging Fearlessly," at thesunchronicle.com/farinella.