In the fourth quarter of Thursday’s game against the Redskins, Giants rookie safety Kenny Phillips tackled Washington wide receiver Santana Moss for a 4-yard gain on third-and-17, keeping him in bounds, keeping the clock running, and all but ending the Redskins’ last chance at a comeback.

In the fourth quarter of Sunday’s game against the Dolphins, Jets rookie cornerback Dwight Lowery deflected two straight passes in the end zone from Miami Dolphins quarterback Chad Pennington, ending a potential scoring drive in a game the Jets would win 20-14.

Those were just a few plays out of dozens that helped the Giants and Jets win their season openers, but they were two plays that disclosed a great deal about the future of the Giants and the Jets. The plays were emblematic of the way both the Giants and the Jets have stocked their defenses with young, athletic, and aggressive defensive backs, a group of players who are all 26 or younger and should be the nucleus of a couple of good pass defenses this year and for several years to come.

The Giants have so much depth in the secondary that Phillips hasn’t been able to crack the starting lineup, even though he was this year’s first-round draft pick and is by all appearances a star in the making. For now, the 21-year-old Phillips starts the game on the bench behind a couple of safeties who joined the Giants with significantly lower expectations but who have proven themselves to be more than capable at a young age.

James Butler, who came to the Giants as an undrafted free agent in 2005, got the start at strong safety on Thursday, and he showed that he can be a force against the run. Butler, a 25-year-old who became a starter last season after two years contributing mostly on special teams, tackled Redskins running back Clinton Portis five times Thursday night, all after short runs that were well short of first-down yardage.

The Giants’ other starting safety is Michael Johnson, a 2007 seventh-round draft pick who became one of the pleasant surprises of last season. The 24-year-old Johnson started five games on defense as a rookie and played well Thursday, although he’s likely to lose the starting job to Phillips at some point this season.

Starting at cornerback for the Giants are the 25-year-old Aaron Ross, last year’s first-round draft pick, and Corey Webster, a 2005 second-round pick who at age 26 is the old man of the bunch. Only a few teams in the NFL can match the Giants’ youth and talent in the secondary.

The Jets are one of the few. The 22-year-old Lowery far exceeded expectations in his first NFL game; when the Jets took him in the fourth round out of San Jose State, he was viewed more as a project than an impact player. But Justin Miller, who would ordinarily start at cornerback, missed Sunday’s game with a foot injury, and on the basis of Sunday’s game, it seems safe to conclude that whenever Miller is healthy enough to play, he’s unlikely to beat out Lowery for the starting job.

The Jets’ other starting cornerback, the 23-year-old Darrelle Revis, intercepted Pennington’s pass on the Dolphins’ last play to seal the win for the Jets. Revis was a first-round draft pick who started all 16 games as a rookie in 2007, and based on the way he played in the first game of the season, he appears poised to have an even better year in 2008. Revis was matched up one-on-one with Dolphins receiver Ted Ginn for most of the game Sunday, and Ginn ended the day catching just two of the six passes Pennington threw him, for 17 yards.

The Jets are one of the strongest teams in the league at safety, with the 25-year-old Eric Smith and, especially, the 26-year-old Kerry Rhodes. Aggressive plays near the line of scrimmage are Rhodes’s specialty, and on the first play of Miami’s final drive Sunday, Rhodes put the Dolphins in a hole by keeping running back Ricky Williams in bounds as he tackled him for a 2-yard loss.

The Jets’ secondary will face an interesting test on Sunday, when the New England Patriots come to town. A year ago Randy Moss made Revis look bad in his first pro game, catching nine passes for 183 yards as the Patriots embarrassed the Jets at the Meadowlands. But this year, with Tom Brady hurt, the game will be very different. The one-on-one matchup between Revis and Moss will be a great one to watch, although Revis is basically in a no-win situation: He’ll get the blame if Moss plays well, but if he shuts Moss down, everyone will say it’s because Matt Cassel is no Tom Brady.

That’s the way it so often works in the NFL — 22 players are on the field, but everyone focuses on the quarterback. For all the talk in New York about Eli Manning and Brett Favre, however, stopping the other team’s quarterback is just as important as getting good play from your own. With both youth and talent on their side, the Giants and Jets are well suited to stopping the opposing quarterback, both this year and for years to come.

Mr. Smith is a writer for Fanhouse.com