Kurtenbach: The 49ers just beat up two of the NFL’s top lines. That’s a big deal entering winter football season

When the weather turns nasty, the NFL becomes nastier.

Leave that “basketball on turf” nonsense for the sunshine. When it’s cold, and the games really matter, they’re won or lost in the trenches by the big uglies on the offensive line and defensive line.

It warms my heart.

If you’re a 49ers fan, watching the performance of San Francisco’s offensive and defensive lines in Sunday’s win over the Eagles likely warmed your heart, too.

Both units were outstanding. And that should set a tone for the rest of the season, as the Niners fight for the NFC’s No. 1 seed.

I won’t lie: I didn’t see that kind of dominant performance coming on either side of the ball.

In fact, the top concern I had for the Niners heading into Sunday’s game with the Eagles was how they would fare in that trench battle. I thought the Eagles had a clear advantage on both sides of the ball.

I thought wrong.

The Niners took a bit of time to get going — the first two drives were quite poor for both the offensive and defensive lines — but once both revved up, they controlled the game.

The Niners’ defensive line looked like football’s best again. Nick Bosa was immense. Javon Hargrave and Arik Armstead created an unstoppable 1-2 punch in the middle. Rotating players meant the Niners’ front four came in waves and didn’t require any help to put pressure on Philadelphia quarterback Jalen Hurts, who was not only hurried, but also confined in the pocket on Sunday.

San Francisco had 26 pressures against the Eagles, per ESPN. Twenty-one came with just a four-man rush. Instead of picking fights with Niners linebackers on the sideline, Big Dom could have made himself useful by blocking one on the field.

Jokes aside, Sunday’s game was vintage Niners defense. It was 2019 all over again.

And not only did the Niners’ defensive line dominate with the pass rush, but it was exceptional against the run, too.

Some of this was the scoreline, but the Eagles had only nine designed runs on Sunday. The Niners — particularly Bosa — were so sound in controlling their gaps and so sure as tacklers that Philadelphia abandoned the run long before the game demanded such a tactical change.

It was the defensive line’s best performance of a season that had been up and down the first 12 weeks.

So, for it to come against the NFL’s best offensive line (there’s not even a close second) speaks volumes.

Yes, the 49ers’ defensive line tossed Jason Kelce & Co. around for the final 45 minutes of the game.

“We were thrashing out there,” Hargrave told me after the game. “Those guys are good, but we kept thrashing.”

For a San Francisco team that has built its defensive identity on its defensive line play, Sunday’s game is a massive boost to momentum. The team’s next two games against Seattle and Arizona should only add to the good vibes.

The Niners’ defensive line will need all the good it can get with Baltimore following Seattle and Arizona on the schedule. The Ravens, who come to Levi’s on Dec. 25, boast the second-best offensive line in football and still have a run game unlike any other in the NFL.

The 49ers’ offensive line on Sunday wasn’t as good as the team’s defensive line, but it still deserves massive kudos for its performance.

The Niners had minus-6 yards of total offense in the first quarter. Much of that had to do with poor pass protection and run blocking, particularly on the right side of the line.

But head coach and offensive play-caller Kyle Shanahan made a few in-game changes, and the line thrived for the remainder of the game, pushing around a physical and immensely talented Eagles front.

The big move for Shanahan was to run to the left side. That’s where Trent Williams, the NFL’s best left tackle, works and he had a half-dozen highlight blocks Sunday. This might sound strange, but the pairing of him and running back Christian McCaffrey is second to none in the NFL right now. They just work so well together.

But amid that obvious move to start moving the ball in the run game was the movement of offensive linemen in plays.

The Niners are still primarily a zone-blocking team, but Shanahan started calling for more gap blocks in the run game, and it opened up some massive holes, with everyone on the line having a highlight or two.

It’s the first time all season I’ve positively noted every offensive lineman in my notes during the game.

With that and enough pass protection for quarterback Brock Purdy to see enough of the field to get the ball to Deebo Samuel (Purdy was only sacked twice), the Niners scored six consecutive touchdowns for the first time since 1992.

Now, let’s be clear: The Eagles faded hard, a somewhat expected turn in their third game in 13 days and just one week after the defense played 90-plus snaps.

That will be Philadelphia’s excuse. It’s a valid one — but only to a point, because the Niners’ performances in the trenches were valid, too. They took on arguably the best trench team in football and beat them, handily, on both sides.

And if that doesn’t convince you that the Niners’ are the NFL’s team to beat this winter, I don’t know what will.