Washington State led 47-26 at the half after shooting 60.6 percent from the field and holding Texas Southern to 32.3 percent. The score was tied at 15-15 when the Cougars took control of the game with an 11-0 run midway through the half.
Riley scored 19 points in the second half, when the Tigers shot 57.7 to finish at 43.9 for the game. The Cougars shot 55.2 percent in the game, helped by a 28-2 advantage in bench points. Hawkinson, a regular starter, came off the bench after missing the previous game with a groin injury.
The Cougars' 4-0 start is their best since 2010, when they started 5-0. WSU's opponents have a combined record of 5-17. The Cougars' next game is Wednesday at home against 10th-ranked Gonzaga (4-1).
Texas Southern: Partly for financial reasons, the Tigers are playing all 13 of their nonconference games on the road. The Tigers don't play their first game at home in Houston until Jan. 2, when they open Southwestern Athletic Conference play against Southern (La.).
Washington State: The Cougars play their first six games at home, then travel just 8 miles to visit Idaho. Two more home games follow before WSU plays three games at the Diamond Head Classic in Honolulu. The Cougars then start Pac-12 Conference play with three games at home. Coach Ernie Kent said he wanted to go with a softer schedule early to help break in seven new players.
Texas Southern visits Mississippi State on Tuesday.
Washington State hosts No. 10 Gonzaga on Wednesday.