LOS ANGELES -- Daven Harmeling wasn't about a let a broken thumb on his shooting hand get in the way in No. 4 Washington State's biggest test of the season to date.

The 6-foot-7 junior came off the bench to score 14 of his season-high 19 points in the first half, Aron Baynes had 18 points and nine rebounds, and the undefeated Cougars beat Southern California 73-58 on Thursday night to give them their best start in 91 years.

"I've been in a shooting slump nearly all year long," said Harmeling, who brought a 6.4 scoring average into the game, having made only 26 of 61 field-goal attempts (42.6 percent) including 7 of 27 (24.1 percent) from 3-point range.

He shot 7-for-10 against the Trojans including 5-for-7 from beyond the arc.

Harmeling wore a soft cast with padding on his thumb, which he broke Dec. 21, causing him to miss two games. His big first half sparked the Cougars to a 27-23 lead.

"I felt we were a little stagnant on offense; we needed a lift, give us a little bit of energy off the bench," Harmeling said.

"Daven has the capacity to come in and light it up, really stretch the defense," said Taylor Rochestie, who had 12 points and seven assists.

The Cougars were outstanding offensively in the second half, shooting 16-for-26 (61.5 percent) and committing only two turnovers. That enabled them to win handily despite USC's 15-of-22 second-half shooting.

"They were aggressive, but they had a poise about them, a patience. It was just good basketball -- it was a complete second half offensively," said Washington State coach Tony Bennett, whose team is known more for its defense than offense.

Derrick Low added 10 points and five assists for the Cougars (14-0, 2-0), who beat USC for only the 12th time in 53 road games.

WSU, the highest-ranked team in the Pac-10 for the first time, hasn't won a conference championship since 1941. The Cougars are off to their best start since the 1916-17 team won its first 15 games.

Now, the Cougars will face an even bigger test Saturday, completing their visit to Los Angeles at Pauley Pavilion against No. 5 UCLA (15-1, 3-0) in the sixth-ever Pac-10 game matching two teams ranked in the top five. The Cougars have won only once in 50 road games against the Bruins.

"They play with poise. We play with a lot of new guys," USC coach Tim Floyd said. "We hope to get to that point. I don't remember them taking a bad shot, and I recall we did a few times."

O.J. Mayo, the Pac-10's leading scorer, led USC (9-6, 0-3) with 22 points and seven rebounds. Taj Gibson and Dwight Lewis added 16 points each for the Trojans, giving those three all but four of their team's points.

Davon Jefferson, USC's second-leading scorer with an 11.9-point average, sat out the game.

"He didn't make the cut tonight. It was a coach's decision," Floyd said. "He's a young player, and there's a lot of room for growth."

Floyd wouldn't comment when asked if Jefferson didn't play because of disciplinary reasons, but did say he expected the freshman to play Saturday against Washington.

Low made two 3-pointers during a 15-4 run that gave the Cougars a 45-33 lead with 12:21 remaining. Kyle Weaver, WSU's second-leading scorer, got his first four points during the spurt.

Baskets by Lowe and Rochestie made it 54-40 with 8:16 remaining, and the Trojans weren't closer than eight points after that.

USC didn't shoot a free throw until Mayo made two with 4:43 left, trimming the Cougars' lead to 58-48. The Trojans wound up going 4-for-4 from the line to Washington State's 13-for-18.

It was 64-50 before the Trojans scored six consecutive points to draw within eight with 2:54 to play. But Baynes dunked off a pass from Low as the shot clock wound down, USC's Daniel Hackett missed a 3-pointer, and Rochestie made two free throws with 1:52 left to put the game out of reach.

"The difference was they were more poised," said Mayo, who committed five of USC's 13 turnovers. "They pretty much stayed steady. Any shot they wanted, they got."

The Cougars shot only 9-for-27 in the first half, but went 7-for-12 from 3-point range in taking their four-point lead. Harmeling was 4-for-5 and Rochestie 2-for-2 from beyond the arc.

The Cougars led 16-12 when both teams hit a dry spell, going scoreless for over four minutes before Harmeling made a jumper.

A basket by Mayo ended a 5½-minute USC scoring drought and triggered a 9-0 run that gave the Trojans a 21-18 lead, but Harmeling responded by making three consecutive 3-pointers to put his team ahead for good before Mayo set Gibson up for a dunk in the final seconds of the half.

Washington State freshman Stephen Sauls, who collapsed in practice Monday and was hospitalized, did not make the trip. Sauls, averaging 2.1 points in eight games, was released from a Pullman hospital Thursday.