The first of Mike McCarthy's goals has been completed by getting the Green Bay Packers to a 4-0 record. But in a league that's all about "what have you done for me lately," the Packers know they can't relax now – especially not with St. Louis stepping confidently into Lambeau Field after the Rams gave the Arizona Cardinals their first loss last weekend. 

Here are five keys things to watch in Sunday's Packers-Rams game.

1. Chance for the Packers' run defense to make it four in a row

Marshawn Lynch, Jamaal Charles and Carlos Hyde combined for 110 rushing yards against Green Bay over the past three games. Lynch and Charles are easily two of the five best running backs in the NFL, and Hyde entered Week 4 with the league's third-most rushing yards. But in each of those games, the Packers' run defense won the battle.

"We’re very, I don’t want to say satisfied, but we’re very pleased with our run defense – outside of Week 1 – thus far," nose tackle B.J. Raji said.

There's been an obvious and significant turnaround since Green Bay allowed Matt Forte to rush for 141 yards to open the regular season. And in Raji's opinion, it's a direct result of Clay Matthews' skill set and how that's helped the defensive linemen.

"I think upfront we feel like we can take more chances because (the inside linebackers this season) are athletic enough, and they’re sensible enough to play off of us," Raji said. "Whereas in the past, that wasn’t always the case."

Now, the Packers have another challenge in the form of St. Louis running back Todd Gurley. He doesn't have the name recognition of Lynch or Charles yet, but Gurley should soon find himself in that group. Gurley was the 10th overall pick in this year's draft, and he's coming off a game in which he ran for 146 yards on 19 carries (7.7 average).

2. Getting Green Bay's offense back in sync

Aaron Rodgers admitted after Green Bay's win in San Francisco that the Packers offense wasn't its normal self. Rodgers continued to not turn the ball over, and Green Bay did run for an impressive 162 yards. But everything seemed a bit off. 

As injuries have mounted on offense, it hasn't been easy for Rodgers and company to just keep moving along as if nothing changed. Davante Adams played three snaps in Week 3 before his ankle injury worsened. Adams missed last week's game, and it's unlikely he plays against St. Louis. Jordy Nelson is spending the entire season on injured reserve. Tight end Andrew Quarless is on injured reserve with designation to return. Randall Cobb has been playing through a shoulder injury that even he doesn't expect to get back to 100 percent. And now James Jones has been a limited practice participant with a hamstring injury.

The Packers won't be any healthier in their wide receiver or tight end groups this week than they were against the 49ers. Somehow, Rodgers will have to get the offense rolling again despite the injuries.

3. Unlocking the "Jordy Package" without Nelson

Nelson led Green Bay in yards per reception each of the past four seasons. He had a career-best 18.6 yards per catch in 2011 and has been no lower than 15.2 yards per reception since 2011.

Compared to previous seasons, the big plays haven't been as frequent for Rodgers this year. There's no doubt in Rodgers' mind that it has a lot to do with Nelson's absence.

"We’ve still had some balls over the top, but we just haven’t had kind of the ‘Jordy package,’" Rodgers said. "We haven’t found a guy to do some of that stuff yet."

Jeff Janis has the speed to get open downfield, but he doesn't have a catch yet this season. Montgomery can get separation, but he's still only four games into his professional career. Cobb has mostly operated out of the slot and the backfield. Tight end Richard Rodgers isn't going to be running many deep routes. And even though Jones leads Green Bay in yards per catch so far this season, he's 31 years old and more of a possession receiver.

In order to stretch the field like the Packers used to with Nelson, one of the receivers is going to have to prove to Rodgers that he can get separation and come down with the ball on a deep pass.

4. Bryan Bulaga and Don Barclay

Don Barclay has not filled in very well at right tackle over the past three games. According to data from ProFootballFocus, Barclay has allowed the most quarterback hurries out of any offensive tackle in the NFL. Keep in mind, Barclay didn't even play Week 1 in Chicago. So, he's allowed more pressures than the rest of the league's offensive tackles despite playing fewer snaps.

Somewhat surprisingly, Bryan Bulaga is trending in the direction of being available to play Sunday. That would send Barclay back to the bench, thus providing an immediate boost to the offensive line. 

Bulaga is only three weeks removed from having suffered an MLC injury to his left knee in practice. The injury could have sidelined him for up to six weeks, but his rehabilitation has been ahead of schedule.

5. An elite Rams defensive line

Bulaga could be returning just in time, as St. Louis boasts a defensive line that consists entirely of former first-round picks.

Aaron Donald is playing every bit as dominant as J.J. Watt is, and Robert Quinn and Nick Fairley are both creating a ton of pressure on quarterbacks this season.

The Rams have 17 sacks this season, so they're averaging at least four sacks per game. That's tied with Green Bay for the second-most sacks in the NFL.