TEMPE, Ariz. >> Arizona State’s defense had been one of the worst in the country the past two years and it looked as if nothing would change at the start of this season.

The Sun Devils continued to miss assignments, give up big-chunk plays, allowed more than 500 yards twice and gave up 301 yards to Stanford’s Bryce Love in their first three games.

Then something clicked. Players meshed on the field and started sticking to their assignments. The big plays disappeared. Arizona State shut down No. 5 Washington, did the same to Utah a week later.

In a season that once seemed hopeless, the Sun Devils have put themselves in a position to take the Pac-12 South lead with a win over No. 21 USC on Saturday.

“We have been through the hard times. I think it builds character and toughness,” Arizona State coach Todd Graham said. “You get to a point where you know what it takes, sacrifice-wise, to get there and these guys have done it. Behind the scenes, I think there is a lot of confidence building with our guys.”

Arizona State (4-3, 3-1 Pac-12) faces what may be its stiffest challenge yet against the Trojans.

USC (6-2, 4-1) has been banged up — 11 starters have missed games — and is coming off a 49-14 loss to No. 9 Notre Dame last weekend.

But the Trojans, led by prolific quarterback Sam Darnold, are a threat to put up big numbers against any team and will be playing angry after last week’s beatdown. Once a national-title contender, USC has lost two of its past four games, all but knocking itself out of the College Football Playoff picture.

“You deal with the realism of where we are at,” USC coach Clay Helton said. “We are a 6-2 football team that leads the Pac-12 South and has the opportunity to play another game and remain in first place in the Pac-12 South. There is still a lot to play for in this season.”

A few more things to look for when Arizona State hosts USC:

TURNOVERS IN TROY

USC has had little trouble moving the ball this season, but also has struggled hanging onto it. The Trojans have 19 turnovers in eight games, second-worst among FBS team, and had three last week against Notre Dame, including a fumble by Darnold on the first play from scrimmage. Arizona State has been adept at creating turnovers during its defensive turnaround, including four interceptions against Utah last week.

ASU’S TIME OF POSSESSION

One reason for Arizona State’s recent success — other than the defensive surge — has been the offense’s ability to control the ball. The Sun Devils enter Saturday’s game 12th nationally in time of possession at 33:08 minutes per game and had a whopping 12-minute advantage against Utah last week.

USC’S OFFENSE

Darnold has thrown for 2,292 yards and 17 TDs while completing 63 percent of his passes with 10 interceptions, including one that led to a touchdown last week. The Trojans have been good at times running the ball this season, thanks to Ronald Jones II’s 672 yards and eight TDs, but had a rough day against Notre Dame, gaining 76 yards on 31 carries. Some of that was falling behind 28-0 by halftime, but the Trojans will need to run the ball better against Arizona State.

PROTECTING MANNY

Arizona State has struggled to protect quarterback Manny Wilkins, but it hasn’t hampered him that much. Wilkins has been pressured on 34.5 percent of his dropbacks, 13th-most nationally. Wilkins has handled the pressure well, ranking 13th nationally with an 88.9 quarterback rating under pressure. Of course, he does better when he has protection, completing 73.6 percent of his passes when not pressured, sixth-best nationally.