Sixth-ranked Southern California turned three first-period turnovers by Illinois into 17 points, including two touchdown passes by Sean Salisbury, and defeated the No. 11 Illini, 20-10, yesterday before 76,369 in Champaign, Ill., in the opener for both teams.

Cornerback Matt Johnson intercepted a poorly thrown pass by Jack Trudeau and returned it nine yards to the Illinois 15 to set up Salisbury's three-yard scoring pass to Hank Norman at 6:09. It was the first of six Illinois giveaways -- four interceptions and two fumbles.

The Trojans, who have won 16 straight against Big Ten teams, made it 14-0 barely 3 1/2 minutes later on Salisbury's 46-yard pass to Randy Tanner. It came on the first play after defensive tackle Matt Koart recovered a pitchout fumbled by fullback Keith Jones. Tanner beat safety Ed White at the five-yard line for the reception.

The Illini promptly made it three turnovers in as many possessions. Trudeau (21 of 37, 310 yards) threw a long pass from his 33 that Junior Thurman intercepted at the Southern Cal 24 and returned to the 33, where he fumbled. The ball was recovered by Illinois' Ray Wilson but the Illini were penalized for an infraction during the interception return and Southern Cal retained possession at its 43.

Six plays later, on the opening play of the second period, Don Shafer kicked a 46-yard field goal to give Southern Cal a 17-0 halftime lead.

"We didn't perform," Illinois Coach Mike White said. "When you're a turnover team, against a good football team, you might as well keep moving.

Illinois, which had won 11 straight at home, didn't cross midfield until its fifth and final possession of the first half. David Williams, the Illini's all-America wide receiver, caught five passes for 50 yards, including a diving third-down catch at the USC one.

Illinois elected to go for a touchdown but linebacker Garrett Breeland deflected Trudeau's short pass away from tight end Cap Boso with 25 seconds left in the half.

"We forced Trudeau to hold onto the ball by giving them different looks in our pass coverage," Southern Cal Coach Ted Tollner said. "Our defense confused them . . . We knew they'd get some yards with their passing game, and they did. We tried to change up a lot with our nickel looks and make Trudeau hold the ball a little longer."

On its first possession of the second half, Southern Cal made its first turnover. Third-string tailback Steve Webster, a freshman, fumbled and linebacker Bob Sebring recovered at the Illinois 17. The Illini needed one play to score. Trudeau threw to Boso, who caught the ball at the Trojans' 40 when cornerback Louis Brock missed an interception. The 230-pound Boso broke tackles by safeties Tim McDonald and Jerome Tyler for an 83-yard touchdown.

Field goals of 23 yards by USC's Shafer late in the third period and 28 yards by Illinois' Chris White early in the final quarter closed out the scoring.