The Seahawks have won nine straight, postseason included, against the San Francisco 49ers, and making it 10 in a row would be big for Seattle's playoff hopes. While the Seahawks (6-5), have enjoyed a pretty strong season after rebounding from an 0-2 start, it has been a tough year for the 2-9 49ers, who came into the year with high expectations, but whose season has been derailed by injuries, including a season-ending knee injury to quarterback Jimmy Garoppolo.

If the Seahawks are going to win a third straight game and further strengthen their playoff chances, these are three key matchups that could make the difference in Sunday's game at CenturyLink Field:  

1. The battle between best friends and former teammates, aka, Sherm vs. Doug.

For more than a decade, Doug Baldwin and Richard Sherman were teammates, first at Stanford and then with the Seahawks, but on Sunday they'll go head-to-head in a game for the first time. And while they won't line up across from each other all the time, it's bound to happen at times during the game, and when it does, it will be must-see TV as two close friends and fierce competitors face off.

"It's an interesting matchup to watch, and we'll see how it goes," Seahawks coach Pete Carroll said. "They have competed as hard as they could compete for a lot of years. Whether this game shows that or not, they've already been to the top of that mountain. I'm sure that there will be times when they line up on each other."

And Sherman facing Baldwin and his former team isn't interesting just because of Sherman's impressive seven-year run with the Seahawks, but also because he's a key part of San Francisco's defense and a player the Seahawks have to be careful testing.

"I still see a really good football player," offensive coordinator Brian Schottenheimer said. "I still see a guy that dissects things really well. I think his ability to pattern read and recognize things is uncanny. I still see a guy playing at a high level. It's been cool to be around the guys that know him, they certainly know him way better than I do. I think it's interesting because they know him, he knows us, and so that's what's going to make for a fun matchup on Sunday." 

The Seahawks obviously will try to establish the run as they have in most games this season, but they know doing so won't be easy against a 49ers defense that ranks 10th in the league in rushing defense, allowing 102.7 yards-per-game. If the Seahawks aren't able to run the ball as well as they'd like, they showed last week that they're more than capable of moving the ball through the air as well, with Russell Wilson throwing for 339 yards and two touchdowns in a win in Carolina. But if the Seahawks do have to throw the ball, they know they'll need to be aware of an old friend wearing No. 25.

"Sherm is as good as it gets as a corner," Wilson said. "He can make a lot of plays, so you've got to know where he is and understand that. I've got a lot of respect for how he plays the game and how intelligent he is."

2. 49ers running back Matt Breida vs. a Seattle run defense looking to clean things up.

When running back Jerick McKinnon went down with a torn ACL just before the start of the season, it was potentially a big blow to the 49ers running game, but thanks in large part to the emergence of second-year back Matt Breida, the 49ers are still running the ball well, averaging 134.9 yards-per-game, the fifth-best total in the NFL.

Breida, who went undrafted out of Georgia Southern in 2017, leads the 49ers with 738 rushing yards and is averaging an impressive 5.8 yards-per-carry. He is coming off of back-to-back 100-yard games, including gaining 106 yards on just 14 carries last week.

"He's really fast and he likes to get on the edge," linebacker Bobby Wagner said. "Our edge is definitely going to be tested. They're going to try to run outside. They have a lot of good runs to complement, have us thinking it's going to be an outside run and then it cuts back. It's definitely going to be a discipline game. It's going to be a game that we need to make sure we're on our fits, but from him it's kind of like he's going to be a fast guy. They're going to try to get him on the edge, they're going to run a lot of stretch plays to see if they can find a crease in the defense and make it a track game. We're fast too, though."

The Seahawks know if they're going to slow Breida down, they're going to have to clean things up with a run defense that allowed 220 rushing yards to Carolina last week.

"Run defense is connected to everybody," defensive coordinator Ken Norton Jr. said. "I think that anytime that anybody runs the ball, everybody has a responsibility on the defense and it comes down to discipline, gap control, effort, attitude—all these things have to work together to have a successful play."

Added Wagner: "We need to do better. It's definitely an area we need to improve on. We pride ourselves on our run defense and it hasn't been up to par. I take it upon myself to make sure that we do that better. We're still making plays that we need to make when the time presents itself but we definitely have to be more consistent when it comes to the run game and a lot of it is just taking our shot and being on our keys and communicating."

3. The turnover battle.

If you look at the Seahawks and 49ers statistically, you might not think their records were all that different. The Seahawks rank 16th in total offense, while the 49ers rank 17th, trailing Seattle by one-tenth of a yard. The 49ers rank 11th in total defense, while the Seahawks are 16th with 9.3 yards-per-game separating the two teams. But there is one stat in which the teams are drastically different, and it's a big reason why the Seahawks having a winning record and are in playoff contention, and the 49ers are 2-9. Through 11 games, the Seahawks have a turnover differential of plus-eight, which is tied for fifth best in the NFL, while the 49ers rank 31st at minus-17. So far this season, the Seahawks are 5-1 winning turnover battle, while the 49ers are plus-1 in their two victories, and minus-18 the rest of the season.

"It has been huge," 49ers coach Kyle Shanahan said on a conference call. "I mean, our defense, I think we've played a little bit, numbers-wise and everything, similar to Seattle. We had a middle of the pack defense and both of our offenses, we haven't done a lot throwing the ball but Seattle is number one, I believe, in running and I think we're fourth right now so we've depended on the run a lot. We've been middle of the pack on defense, which usually gives you a chance to be in every game but when you're turning the ball over like we have and not getting the turnovers on defense, that makes it really tough to win and I think our record shows that."