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SAN DIEGO -- Tarvaris Jackson realizes he'll need a whole lot more practice and study before he can run the Seattle Seahawks' offense with even a fraction of the poise and precision Philip Rivers gives to the San Diego Chargers.

Luckily for the winning Seahawks, Jackson isn't afraid to go back to work.

Rivers went 5 for 6 while leading an 89-yard scoring in his only series for the Chargers, but Thomas Clayton rushed for a tiebreaking 25-yard touchdown with 3:05 left in the Seahawks' 24-17 victory over San Diego on Thursday night in both clubs' exhibition opener.

Jackson passed for 13 yards over two moderately successful series in his debut as Matt Hasselbeck's replacement with the Seahawks, who trailed 10-0 at halftime. The longtime Vikings backup also was sacked twice, and Jackson was long gone by the time undrafted rookie Josh Portis led two late scoring drives capped by Clayton's decisive romp through the San Diego defense.

"I was just trying to get comfortable with a couple of snaps, just trying to get familiar with everybody," said Jackson, who went 3 for 5. "You work out and throw the ball all summer, but it's a whole lot different when guys are coming at you. We had a couple of miscues, and we have things to work on."

Cornell graduate Bryan Walters returned a kickoff 103 yards for a touchdown late in the third quarter for the Chargers, while Mike Tolbert caught an 8-yard scoring pass to cap the opening drive. Rivers was nearly flawless in his first game after starting last season's Pro Bowl, connecting on an exceptional 48-yard pass to Vincent Jackson.

"That's kind of what we wanted to accomplish, but there are certainly things to clean up," Rivers said. "That can give you a false impression of how easy (it was to score). We still have a long way to go, but that's one drive of the game."

The Seahawks signed Jackson as a free agent last month to replace Hasselbeck, Seattle's starter for the past decade. Although he spent the past five seasons in Minnesota with new Seattle offensive coordinator Darrell Bevell, Jackson had just five practices with the Seahawks before his preseason debut with starting receivers Sidney Rice and Mike Williams sitting out.

Jackson coolly completed a third-down pass over the middle to Doug Baldwin on the Seahawks' third play but later was called for intentional grounding while eluding the Chargers' rush. Jackson alertly scrambled for a first down when every Seattle receiver was covered on the next drive, but he was sacked on consecutive plays moments later -- again with every target well covered.

"I thought the quarterbacks did just fine," Seattle coach Pete Carroll said. "We didn't get open a couple of times for Tarvaris early on. He had to move around. He showed us some great stuff. I thought nothing but good things about the quarterbacks all the way through."

San Diego's revamped defense yielded just 85 yards in the first half, but former Chargers backup Charlie Whitehurst led the Seahawks to their first 10 points on the opening drives of the second half. Whitehurst went 14 for 20 for 115 yards, hoping to prove he's an option if Jackson isn't ready by next month.

"Tarvaris is the No. 1 quarterback coming into camp because of all the obvious reasons," Carroll said, citing his familiarity with Bevell's offense. "When Charlie catches up and learns what's going on and is really in command of the offense, then the competition really begins."

Leon Washington rushed for a 1-yard score on the Seahawks' opening drive of the second half, and Portis hit Anthony McCoy with a tying 6-yard TD pass with 4:02 left.

San Diego rookie Scott Tolzien's fumble set up Clayton's go-ahead score, but the former Wisconsin quarterback drove the Chargers to the Seattle 5 in the final minute before his final pass pinballed among several players and fell incomplete.

Not everything went well for the Seahawks, who lost starting left tackle Russell Okung to an ankle injury. Carroll said X-rays were negative, but "something kind of popped in there."

San Diego got a slick return by Walters, a Seattle-area native and an undrafted second-year pro with an economics degree from his Ivy League alma mater. Walters caught the kickoff in San Diego's end zone and ran into a good-sized corridor through the wedge, keeping his feet after Josh Pinkard's flying tackle attempt and outrunning the rest of the Seahawks.

"I was really nervous," Walters said. "It was tough to sleep last night, not really knowing what role you're going to be put into. It was great to make a contribution like that, and it's even better to do it against the team I grew up watching."

Game notes

Walters graduated from Juanita High School in Kirkland, Wash., the former home of the Seahawks' training complex. ... The Chargers committed 10 penalties. ... Chargers first-round pick Corey Liuget had four tackles and occasionally drew double-teams in his debut on the San Diego defensive line.