PULLMAN, Wash. — Cody Kessler threw for 400 yards and five touchdowns and Southern California beat Washington State 44-17 in rainy, foggy conditions on Saturday.

JuJu Smith caught three TD passes for Southern California (6-3, 5-2 Pac-12), which became eligible for postseason play. Nelson Agholor caught eight passes for 220 yards and scored a pair of touchdowns.

Washington State quarterback Connor Halliday, the nation’s passing yardage leader, was knocked out of the game in the first quarter with an unspecified injury and did not return. Washington State (2-7, 1-5) does not publicly discuss injuries.

Freshman Luke Falk replaced Halliday. He threw for 370 yards and two touchdowns, but it was not enough to prevent the Cougars from suffering their second consecutive home loss and fourth in a row.

Southern Cal, coming off a last-second 24-21 loss at Utah last weekend, had 527 yards of total offense to 444 for Washington State. Kessler completed 21 of 32 passes.

Washington State has surrendered 60, 59 and 44 points in its past three home games.

Special teams have been a problem for Washington State all season, and they broke down again early for the Cougars, who went three-and-out on their first possession. Agholor took the ensuing punt and ran untouched through Washington State for a 65-yard touchdown return and a 7-0 lead with 12:13 left in the first quarter. It was Agholor’s fourth kick return for a touchdown, a Southern Cal record.

Halliday was intercepted on the next series by Hayes Pullard, who ran the ball down to the Washington State 19. Kessler hit Smith on a 22-yard touchdown pass to put the Trojans up 14-0 with 10:33 left in the first quarter.

Halliday was injured on the next series, when two players appeared to fall onto him after he threw a pass. He was driven off the field in a cart while strapped to a stretcher. Falk, a walk-on, came in for his first extensive action of the season.

Andre Heidari booted a 37-yard field goal to give Southern Cal a 17-0 lead early in the second quarter.

Washington State, with Halliday out, punted on its next four possessions, and then turned the ball over on downs on the fifth. Starting at the Cougars’ 36, Kessler threw 14-yard pass to Agholor and then a 22-yard touchdown pass to Smith, for a 24-0 lead.

Washington State finally got on the scoreboard late in the first half when Falk hit Robert Lewis with a 9-yard touchdown pass, capping an 81-yard drive, to cut the Trjoans’ lead to 24-7 at halftime.

The Cougars scored the first points of the second half when Quentin Breshears kicked a 27-yard field goal to cut Southern California’s lead to 24-10 with 6:10 left in the third quarter. The kick came after Washington State drove to the Trojan 9-yard line.

But the Trojans came right back, as Kessler hit a wide open Agholor at midfield and the receiver completed an 87-yard touchdown play for a 31-10 lead.

Smith added a 7-yard touchdown reception from Kessler late in the third. Kessler threw a touchdown pass to Steven Mitchell in the fourth.

For the Cougars, Falk threw a late touchdown pass to Isiah Myers.

Kessler has thrown for 25 touchdowns against only two interceptions so far this season.

Halliday, a senior, holds the NCAA single-game record for yards passing (734), set this year against California, plus a slew of school records.

Soutern California tailback Javorius Allen, who leads the Pac-12 in rushing, rushed for at least 100 yards for the sixth straight game, had 114 yards on 19 carries.

Washington State beat the Trojans 10-7 in Los Angeles last year, but Southern California leads the series 59-9-4.