The Baltimore Ravens, Tennessee Titans, and Miami Dolphins all added bigname quarterbacks this off-season, and all three quarterbacks struggled yesterday. But the teams couldn’t be more different: The Ravens’ great defense more than made up for Steve McNair’s play, while the Titans saw some promise but also many flaws in rookie Vince Young, and the Dolphins’ inability to protect Daunte Culpepper essentially eliminated them from contention on the first day of October.

Through four games this season, Mc-Nair and Baltimore’s offense have been mediocre. But the Ravens know their defense has led a mediocre offense to a championship before, and after yesterday’s come-from-behind win over the San Diego Chargers, they look ready to do it again this year.

Chargers quarterback Philip Rivers rarely found open receivers against Baltimore’s secondary, and the Chargers’ line opened few holes for running back LaDainian Tomlinson, who finished with 97 yards but couldn’t help the Chargers sustain any drives, picking up only one first down on 27 carries.

Despite their inability to move the ball, the Chargers’ defense played well enough that they looked poised to win the game when they took over the ball deep in their own territory, nursing a 13–7 lead with 5:29 remaining.That possession was a disaster: Three penalties and three runs up the middle led San Diego coach Marty Schottenheimer to take an intentional safety, reasoning that the two points it gave Baltimore wouldn’t change the fact that the Ravens still needed a touchdown to win.

From a strategic standpoint, the intentional safety was probably the right move. After all, it allowed the Chargers to take a free kick from their 20-yard line, rather than have to punt from their own end zone.And the Chargers figured they could stop the Ravens’ offense from scoring considering that of the Ravens’ nine previous drives, six ended with punts and three ended with turnovers.

But San Diego dropped into a prevent defense, and that brought Baltimore’s offense to life. McNair scrambled for 12 yards and completed four of five passes for 43 yards, including a 10-yard touchdown to tight end Todd Heap with 41 seconds left. McNair had twice as many total yards on that drive as he did in the entire first half, and it was enough for the Ravens to improve to 4–0 and establish themselves an elite team.

Baltimore is now the class of the AFC North, a division it leads by a game after the Cincinnati Bengals suffered a 38–13 loss to the New England Patriots. It’s too early to say the defense will be back in the Super Bowl, but the Ravens could be headed in that direction.

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Young showed some of the talent yesterday that made him the third pick in this year’s draft, but more often he showed that he has a lot to learn before he can pick apart an NFL defense.Young is such a great athlete that in college he rarely faced a linebacker who could run with him, meaning he could always rely on his feet to make the plays his arm couldn’t. In Tennessee’s 45–14 loss to Dallas yesterday, he learned that won’t be the case in the NFL.

Early in the second quarter, Young showed his flaws and his promise on back-to-back plays. He lost six yards on a designed run when he danced around in the backfield rather than running straight through the hole in the line. But he made up for it nicely, firing a beautiful pass down the middle of the field to Ben Troupe for 18 yards on third-and-13. That was the norm throughout the day — bad decisions on some plays, flashes of greatness on others. The bad outweighed the good, though, as Young finished the day with two interceptions, two fumbles, and so much hesitant running that he compiled only three yards on five carries.

On most days Young’s first start would be the story of the game, but of course, another storyline was unavoidable in Tennessee yesterday. First, Cowboys receiver Terrell Owens suited up just two weeks after breaking his hand and five days after overdosing on painkillers. As he so often does, Owens put aside his distracting off-field issues and produced between the lines, catching five passes for 88 yards. Owens will continue to be the biggest story in the NFL for at least another week, as he’ll make his return to his old stomping grounds, Philadelphia, on Sunday.

Dallas moved into a tie for first place in the NFC East, pending Philadelphia’s game against Green Bay tonight, and must be the favorite in the division going forward.The Cowboys’ win (plus the Washington Redskins’ 36–30 overtime win over the Jacksonville Jaguars, which was capped by a spectacular touchdown catch by Santana Moss, who had four catches for 138 yards and three touchdowns on the day) dropped the Giants to last place in the NFC East.

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A 17–15 loss to the previously winless Houston Texans shows that the Miami Dolphins, a few weeks ago considered a sleeper Super Bowl pick, are one of the weakest teams in the league. Daunte Culpepper rarely had time behind Miami’s offensive line. Houston defensive end Mario Williams, the first pick in this year’s draft who had done next to nothing in his first three games, recorded the first sack of his career in the fourth quarter, then shared a sack with fellow rookie De-Meco Ryans on the next play.Culpepper, who’s still not 100% after major off-season knee surgery, has already been sacked 21 times this year.

Miami, now 1–3, was repeatedly burned by Houston’s wide receivers, Andre Johnson and Eric Moulds. When throwing to Johnson and Moulds, David Carr was 13-of-19 for 177 yards and a touchdown. The suspect secondary is one of the many reasons that the Dolphins fell to last place in the AFC East.

“I believe very much in this team,” Dolphins coach Nick Saban said after the game. It’s hard to imagine that anyone else does.

Mr. Smith is a contributing editor for FootballOutsiders.com.