GLENDALE, Ariz. (AP) — The NFC West takes over Monday night football, and this season at least that means defense.

Going into last weekend, the four NFC West teams ranked among the top nine in the league in defense.

San Francisco leads the way at No. 1 with a powerful, smash-mouth group that overwhelms opponents, particularly with its excellent front seven. Arizona counters with a fast, aggressive unit that rates No. 7 in the league.

It may be a league that runs on offense, but defense could well decide the outcome when the 49ers, looking to break open their lead in the division, face the Cardinals, looking to stop a three-game losing streak with one of the worst offenses in football.

Despite all of Arizona’s problems, though, an upset over San Francisco would leave the Cardinals tied with the 49ers atop the NFC West.

The 49ers don’t throw anything fancy at opponents, but what they do on defense, they do exceedingly well.

“Up front they’re really good,” Arizona quarterback John Skelton said. “Their linebackers are some of the best in the league.”

The secondary must not be too bad, either, since San Francisco is first in the NFL against the pass.

Up front, San Francisco’s trio of Ray McDonald, Isaac Sopoaga and Justin Smith might be able to put tremendous pressure on Skelton without any help, considering Arizona’s woeful offensive line. Add outside linebackers Ahmad Brooks and Aldon Smith, inside backer NaVarro Bowman, then the best of them all, inside linebacker Patrick Willis, and this could be the game’s best front seven.

“They have a solid core. Their front seven, you really can’t find a weak spot,” Arizona running back LaRod Stephens-Howling said. “They’re solid and they stick to their scheme and they do it well. We definitely need both passing and run working to be successful with these guys.”

Considering the Cardinals are one of only three teams averaging less than 300 yards per game — and have been sacked 35 times, nine more than anyone else in the league — Arizona’s only chance Monday would seem to be to keep the score low.

Which brings up the Cardinals’ defense.

The up-front trio of Dan Williams and self-proclaimed 49er haters Darnell Dockett and Calais Campbell are formidable. The outside linebackers Sam Acho and O’Brien Schofield are fast, inside linebacker Paris Lenin is an old-school veteran playing the best football of his career — and inside backer Daryl Washington is an emerging NFL star. In the back end, cornerback Patrick Peterson is off to a strong sophomore season, perennial Pro Bowlers Adrian Wilson still is dependable at strong safety and Kerry Rhodes, bothered by a back injury, should be back at free safety. The problems have come at the other cornerback, where William Gay has struggled and Greg Toler is out with a hamstring injury.

Their effectiveness is amplified by the schemes concocted by defensive coordinator Ray Horton. The Cardinals are fourth in the league in sacks with 21.

“They play fast and in in the second year of that scheme, running around and they can create pressure when they want to,” 49ers quarterback Alex Smith said. “They confuse a lot of quarterbacks. On film, you can see that. They do a lot of unorthodox things and really have some success doing it.”

While the Cardinals are fourth in the NFL against the pass, they’re only 20th against the run. In the last two games, they’ve given up 165 yards against Buffalo and 166 against Minnesota.

“These guys do a lot of great things in the run game to kind of keep teams honest,” Peterson said. “And if you’re not honest in the run game, the play-action comes alive and they try to go deep on you over your head.”

Now they run into the No. 2 running team in the league, one averaging 5.9 yards per carry, led by bruising veteran Frank Gore, who is coming off his 31st career 100-yard game, 131 in 16 carries in a 13-6 win over Seattle.

“It’s not easy,” San Francisco defensive coordinator Greg Roman said. “We see a lot of eight-man fronts. We have since day one.”

Roman often will bring in an added big blocker to help the already terrific offensive line.

Smith has not been at his best lately. The San Francisco quarterback was intercepted three times in a 26-3 home loss to the New York Giants, then last week against the Seahawks, he completed 14 of 23 for 140 yards, with one TD and one interception.

Those were some pretty good defenses. Now he faces another one.

With the NFC West defending so well, he faces the prospect of facing them twice a season.

“It’s great for the stats,” Smith said sarcastically.

The defensive stats, for sure.