Below are the ESPN Football Power Index rankings for Sept. 29, after Week 3 of the 2015 NFL season. For a full explanation on how the FPI is put together, please read this explainer. For more background, you can also read this Q&A.

A few notes heading into Week 4:

There is a new No. 1 in the NFL FPI: the Arizona Cardinals (plus-8.2), up from fifth. With 126 points in their first three games, the Cardinals are tied for the fourth-most points in the league.

Perhaps surprisingly, though, the Cardinals’ defense is contributing more than their offense. The defense is expected to add about 4.3 points per game to the team’s net scoring margin, more than an average team’s defense. The 4.3 defensive FPI rating is tied for second with the Philadelphia Eagles, behind the Denver Broncos (4.5).

Also climbing were the Buffalo Bills (plus-4.6), who moved up six spots to No. 5.

The New England Patriots (plus-8.1) remained No. 2 in FPI after gaining 3.3 points following Week 3’s games (including their 51-17 victory over the Jacksonville Jaguars). At plus-8.5, the Patriots’ offensive FPI rating is best in the NFL.

The Pittsburgh Steelers (plus-3.1), who lost quarterback Ben Roethlisberger to a knee injury Sunday, fell four spots to eighth in FPI. ESPN’s FPI accounts for Roethlisberger being sidelined for four to six weeks.

Notwithstanding his injury, the Steelers’ game Thursday night against the Baltimore Ravens is projected to be the best of Week 4, with a pregame matchup quality of 65.6. FPI gives the Steelers a 56 percent likelihood of beating the Ravens.

The Miami Dolphins fell six spots and the Detroit Lions five in the FPI rankings.