SANTA CLARA, Calif. — A Seahawks team that for most of the past decade had one of the best and most stable safety tandems in NFL history — Earl Thomas and Kam Chancellor — made yet another change in that area for the game Monday night against the 49ers in the latest attempt to solidify a shaky secondary.

Quandre Diggs, acquired in a trade with Detroit last month, got the start at free safety in what was his first action with the Seahawks with Bradley McDougald going to strong safety. Diggs responded with a third-quarter interception.

(Rich Boudet / The Seattle Times)

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It was the fifth different starting safety tandem in 10 games for Seattle after the Seahawks basically went from 2011-17 with just one pair — Chancellor at strong and Thomas at free.

The Seahawks went with McDougald at strong safety and rookie Marquise Blair at free safety last week against Tampa Bay.

But with the Bucs putting up 34 points on Seattle — the most allowed this year by the Seahawks — Seattle coach Pete Carroll instead opted for a more veteran duo against the 49ers.

McDougald entered the game with 68 starts in his career, including 23 the past two years with Seattle, while Diggs has 40 starts in a career that dates to 2015, all with Detroit, including 15 last season and five this year before being traded to Seattle on Oct. 23. Blair has just three starts, the past three weeks, and rookie Ugo Amadi — the only other safety who was active for the game — has none. Lano Hill, the only other safety on the 53-man roster, was inactive due to an elbow injury.

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Seattle dealt a fifth-round choice to the Lions for Diggs. He then missed his first two games with a preexisting hamstring injury.

Seattle had to pick up the rest of his contract, which pays him $1.5 million for the rest of the season.

Seahawks don’t activate Dickson, and Willson then gets hurt

The Seahawks could have made a move before the game to activate tight end Ed Dickson off injured reserve but did not.

That proved costly when Seattle lost starting tight end Luke Willson to a hamstring injury in the first half, leaving the Seahawks with just one tight end — Jacob Hollister.

Dickson had knee surgery in August but returned to practice two weeks ago, and Seattle could have put him on the 53-man roster for the game Monday.

But that also requires waiving someone, and Seattle apparently didn’t want to do that yet.

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But expect Dickson to be activated this week, which will be the deadline for him to return to the active roster.

Jaron Brown among Seattle’s inactive players

Seattle’s list of seven inactive players included veteran receiver Jaron Brown — who lost his spot in part due to the addition of Josh Gordon — and defensive end L.J. Collier, the team’s first-round draft choice last April.

Brown being inactive was something of a surprise given that he has been a regular in the team’s receiving rotation all season.

But the Seahawks generally have had just five receivers active each week, and one of those spots Monday went to Gordon, whom the Seahawks claimed off waivers Nov. 1 and who saw his first action as a Seahawk against the 49ers.

Along with starters Tyler Lockett and DK Metcalf, Seattle’s other two active receivers were David Moore and Malik Turner.

Gordon didn’t start — Moore officially was a starter alongside Metcalf and Lockett — but he played throughout the first half though he did not have a pass thrown his way.

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Brown had seen his playing time drop to just 28% and 23% of the snaps the past two weeks, his lowest of the season, and he also is not on as many special teams as is Turner, which is probably why the Seahawks went with Turner (rookie John Ursua also was again inactive).

Brown signed a one-year deal worth $1.5 million in September after having been released in the cutdown to 53 as Seattle wanted an open spot for some other roster juggling.

Brown has 14 receptions for 205 yards and two touchdowns but had no catches the past two weeks.

As for Collier, this is now the third time this year he has been a healthy inactive (and fourth overall, sitting out one game due to injury). He had been active the past four weeks.

But Quinton Jefferson, who missed the past two weeks with a hip injury, now is healthy and Seattle went with eight defensive linemen, with Collier being the odd man out.

Seattle’s other inactives included two injured players — Hill and guard Phil Haynes.

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Also inactive were cornerback Akeem King and running back C.J. Prosise.

For the 49ers, key players tight end George Kittle and cornerback Ahkello Witherspoon were inactive.

Kittle, the 49ers’ leading receiver with 46 receptions for 541 yards, suffered ankle and knee injuries last Thursday against Arizona.

Witherspoon entered the year as the 49ers’ starting right cornerback but has not played since Week 3 due to a sprained foot. However, he returned to practice this week and had said he was hopeful of playing.

Instead, with Witherspoon out, Emmanuel Moseley again got the start at right corner.

With Kittle out, Ross Dwelley got the start at tight end.

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Shaquem Griffin sees first defensive action of season

Shaquem Griffin, a second-year linebacker for the Seahawks, saw his first action this season, playing throughout the first half in obvious pass-rush situations.

Griffin has been a regular on special teams all year but had yet to play on defense before lining up on a third-down play in the second quarter rushing from the edge.

With Seattle’s pass rush having been an obvious issue all season, Carroll was asked this week about Griffin potentially getting some snaps as a rusher. Carroll said only, “He’s always competing to help.”

But in a game in which the Seahawks obviously were pulling out all the stops, the team gave Griffin a shot.

Griffin is listed as the team’s backup strongside linebacker behind Mychal Kendricks.