It must be a Harbaugh thing.

Jim and John Harbaugh are now a combined 3-0 against the Pittsburgh Steelers, who are 10-1 against every coach not named Harbaugh.

Or maybe it’s a turnover thing.

The Steelers turned it over four times, leading directly to 13 San Francisco points in the Niners’ 20-3 victory Monday night at Candlestick Park.

Or maybe it’s just a Roethlisberger thing.

With their franchise quarterback ailing, the Pittsburgh offense failed to establish any momentum, falling as Ben Roethlisberger tossed 19 incomplete passes and three interceptions — two coming when the game was still well within reach on bad, un-Ben-like passes. With San Fran’s top-ranked run defense holding Rashard Mendenhall and the Pittsburgh running game in check, there was just too much pressure on Roethlisberger, who took a slew of hits down the stretch and failed to make the throws he usually makes.

Either way, the Steelers failed to take advantage of a blowout Baltimore loss on Sunday night by falling in a game that probably decided their playoff destiny on Monday night. Had they won, they would have only had to beat the terrible Rams and terrible Browns to finish the year as the AFC’s top seed.

Instead, they’re now likely to settle for a wild-card spot.

Meanwhile, the 49ers took another big step toward wrapping up a first-round bye. If they can win out as favorites against Seattle and St. Louis, they’ll be the No. 2 seed in the NFC.

Thoughts on a wacky, weird Monday nighter…

Turnovers continue to kill the Steelers. They came in with a turnover ratio of minus-7. With Roethlisberger clearly struggling due to his injury, that number dropped by four, with Big Ben committing all four turnovers. The way Roethlisberger looked, it wouldn’t be surprising to see him sit Saturday against St. Louis. The Steelers might have to settle for the fifth spot in the AFC.

Turnovers continue to be key for the Niners. Takeaways were again their bread and butter Monday night, as they scored 13 points off of two picks and a fumble in the victory. At plus-25, they have the best turnover ratio in football, five clear of second-place Green Bay. Alex Smith has thrown just five interceptions all year, and he played a clean game against a dangerous defense. He and Frank Gore have turned it over just nine times on 722 pass/rush attempts this season. That’s why Jim Harbaugh is your 2011 coach of the year.

San Francisco fixes its biggest weakness. A team that had just three touchdowns in its last 19 trips to the red zone coming into this game settled for two more field goals inside the Pittsburgh 20 in the first half. But then they finally delivered with two red-zone scores in the second half. Against a very stout Steelers defense, that’s promising.

You have to commend Roethlisberger for playing. He had some luck on his side — had the injury taken place last Sunday instead of last Thursday, I doubt he’d have played. But it was still quite a gutsy effort. Would the Steelers have been better off without him? Maybe. Would they have won without him? It’s highly unlikely.

That said, why was he on the field in the final minutes, taking a beating from the San Fran pass rush? I have no idea what Mike Tomlin was thinking by allowing that to be the case with Pittsburgh trailing by three scores with less than five minutes to play against a fierce pass rush. On the road and against a defense his team had scored three points on all night, there was no way anything good was going to come of that.

About those blackouts. Not to be a conspiracy theorist but the team is still in the process of pushing its new stadium, and both power outages took place at safe times, while ESPN was in commercial break. Verrry interesting. But seriously, thank goodness they didn’t take place during plays. That could have been disastrous. I’ll admit it was sort of cool watching as the unique circumstances transpired as we lost 36 minutes to delays, especially when Ben Roethlisberger was heard asking “Where’s James Harrison when you need him” as a fan dashed onto the field. I assume he was alluding to this:

Tough luck for ESPN. The previous five Monday Night Football games dating back to Week 10: Packers 45, Vikings 7; Patriots 34, Chiefs 3; Saints 49, Giants 24; Chargers 38, Jaguars 14; Seahawks 30, Rams 13. This week, they finally land a marquee matchup, and they get 36 minutes of delays due to circumstances out of their control. Then again, as my good acquaintance Will Farquharson noted to me, “Who cares about ESPN’s ratings?”

Two more power outage-related questions: 1. Couldn’t they have used TV timeouts during the stoppages to fill their quotas and then brought us the rest of the game with fewer commercial breaks than normal? Maybe that would’ve pissed off the sponsors, I don’t know. Would’ve been nice. And 2. What’s with this mysterious penalty that took place at the start of the second outage?

San Fran did a better job replacing a missing linebacker than Pittsburgh did. Without James Harrison, the Steelers failed to register a sack or a turnover and were gashed by Frank Gore in crunch time. Without Patrick Willis, the Niners got three big plays from no-name replacement Larry Grant and looked as though they weren’t missing a beat. At least Harrison tried to make a difference off the field…

And now LaMarr Woodley is hurt. At least Harrison’s back from suspension next week, but Pittsburgh has just been down too many men this year. It’s going to be tough to overcome, especially if Woodley has to miss more time. Then again, we said similar things about the wild-card Packers last year at this time.

Von Miller is getting a run for his rookie-of-the-year money. Hard to believe, but Miller no longer leads rookies in sacks after Aldon Smith had a 2.5-sack performance Monday night. Smith now has 13 on the season, only 1.5 back of Jevon Kearse’s rookie record. Both Miller and Smith have emerged as Pro Bowlers right off the bat. Considering what Cam Newton, Andy Dalton, A.J. Green, Patrick Peterson, Marcell Dareus, Julio Jones, J.J. Watt, Robert Quinn, Ryan Kerrigan and Adrian Clayborn have also done, it’s been real hard to find a bad rookie this year. The future looks bright for the 2011 class.