Chris Petersen had a breakthrough moment in his Washington career Thursday night at USC. / Drew McKenzie, Sportspress Northwest file

The only misstep coach Chris Petersen made in the run-up to the USC game was rhetorical, saying the 17th-ranked Trojans were “very underrated.” No, they weren’t. But the freshman-pickled Huskies had to prove him wrong. As important, they had to prove that Petersen’s program was going in the right direction by delivering a signature win.

Until Thursday night, the Huskies under Petersen beat only the teams they were favored to beat, and lost every game in which opponents were favored. But as an ESPN national television audience, which included many kids in the fertile recruiting grounds of the Southland, watched, the 18-point underdog Huskies delivered on the optimism that surrounded Petersen’s hire with 17-12 grinder of a triumph at the legendary Coliseum.

Two freshmen, QB Jake Browning and RB Myles Gaskin, gave the offense just enough to survive while the defense powered down a Trojans offense that led the Pac-12 Conference with 47 points a game.

Just as important, Huskies fans can offer their thanks to Steve Sarksian for three things:

• Coming to Washington in 2009 to restore respectability to a tattered program;
• Leaving Washington after 2013 before he lost respectability;
• Arriving at USC to coach a dumb game that helped Washington climb the college football ladder.

Why Sarkisian kept forcing his playcalling to QB Cody Kessler’s passing, when the Huskies defense had him made, while ignoring a running game that gashed UW several times, will remain one of the great mysteries of the Pac-12’s second century.

But at least he was honest about it, which is a valued trait for anyone who might be a recovering alcoholic.

“We didn’t coach well enough and play well enough to win the game,” he said. “This one at end of the day is on me.”

Meanwhile, Petersen, his roster loaded with players from the greater Los Angeles area, most of whom would have sold their souls for a chance to be a Trojan, reveled in helping deliver the next-best thing: Beating the Trojans.

“The guys are fired up,” he said. “They have a lot of respect for the USC players, coaches and program. That’s why they’re excited.”

Half of the roster was recruited to Washington by Sarkisian, whose dash to his “dream job” of USC in 2013 left some genuinely hurt feelings. But expression of those feelings in words is not allowed in the macho protocol of college football.

But deeds? That’s OK.

Deeds were especially apparent from the defense, which sacked Kessler on USC’s first play from scrimmage, the first of five throw-downs of the one-time Heisman Trophy candidate. He was picked twice and the Trojans were held to an astonishing 1-for-13 on third downs.

The second consecutive home loss (Stanford won 41-31 two weeks ago) for USC produced heavy boos and early departures from impatient fans who have been cool to Sarkisian’s hire almost from the beginning.

“This is going to test the character of a lot of guys,” Kessler told reporters after the game. “This one hurts. It hurts. I’m not going to lie.”

The two biggest defensive moments came after USC’s only touchdown drive of the game concluded with a one-yard run by RB Ronald Jones to cut the lead to 17-12 with 12:02 left in the game. The UW offense went three and out to help swing the momentum heavily in favor of USC.

With plenty of time left to sustain a drive on the ground for a go-ahead touchdown, USC inexplicably called three passes, only one of which was completed, for four yards. A secondary enhanced by the return from injury of CB Budda Baker offered great coverage while Kessler was pressured to throw quickly. The Trojans punted.

The Huskies again went three and out, and this time the Trojans traveled all the way to the Washington 25-yard line. But on third-and-five, Kessler was sacked a fifth time, this by LB Travis Feeney. The yardage loss was critical, because PK Alex Wood, a walk-on from Mercer Island High School, missed a 46-yard field goal when the ball hit the crossbar with 3:44 left.

Petersen was thrilled with the defensive feat, particularly after the Huskies offense came away empty from three drives in the first quarter that began on the USC side of the field, surely an omen for eventual failure. But no.

“We got some heat on Cody, and our secondary was right there on them, contesting everything,” he said. “We tackled well and hunted in packs.

“We had a great energy. Sometimes when you start fast, you wear down. They didn’t. There’s lots of lessons to be learned tonight.”

Perhaps the biggest lesson was that, contrary to the grumblings from some Huskies fans, the Washington job was not too big for Petersen and his staff, imported nearly intact from Boise State.

Another lesson might be that the USC job might be too big for Sarkisian, who had just learned an equally embarrassing lesson in August: Never mix alcohol with meds.

He may also have learned that in moving from job to job, it is best to go out of conference, so the hurt feelings left behind have a harder time catching up.