Patrick Willis and the rest of the San Francisco defense were fine without a couple of key players, at least for the opener against Dallas.

The 49ers scored on the second play on Chris Culliver's 35-yard fumble return and gave Colin Kaepernick the ball at the Dallas 2 on one of three interceptions of Tony Romo before halftime in a 28-17 win over the sloppy Cowboys on Sunday.

For all the talk about Aldon Smith's nine-game suspension over off-the-field issues and fellow linebacker NaVorro Bowman being out until midseason because of a knee injury, the defense looked a lot like the units that helped carry the 49ers to three straight NFC championship games.

"Everyone that's been talking about our defense, about how we won't be as good and what not, I don't get caught up in all that," said Willis, a linebacker who picked off a pass intended for Jason Witten in the San Francisco end zone. "The only thing that matters to me is how we perform on the field on game day with whoever is on the field."

Defensive tackle Ray McDonald was among those on the field a week after he was arrested in a domestic violence case, which came within days of Commissioner Roger Goodell announcing stiffer penalties in such instances. The 49ers have said they believe the facts support allowing McDonald to play while the legal process plays out.

All this after the team waited all summer to find out how long Smith would be banned following his most recent run-in with the law — an arrest at Los Angeles International Airport for being uncooperative with TSA agents and telling them he had a bomb.

"There's been a lot of rhetoric," said coach Jim Harbaugh, who improved to 4-0 in season openers. "This game was about steel in the spine. When it comes to 49er players, that's where they excel."

After Culliver picked up a loose ball stripped from DeMarco Murray and ran untouched for a score, safety Eric Reid returned Romo's first interception 48 yards to the Dallas 2, setting up Kaepernick's second scoring toss to Vernon Davis on the next play.

Things to know after the 49ers built a 28-3 halftime and held on from there:

RAGGED ROMO

Romo looked like a quarterback who was limited in the offseason and training camp, not a good start for a team trying to avoid tying a franchise record with a fifth straight year of missing the playoffs.

He didn't see Reid on a throw to Dez Bryant, then didn't see wide-open receiver Dwayne Harris for what would have been an easy touchdown. Instead he forced the pass that Willis intercepted.

"I felt comfortable," said Romo, who threw for 281 yards and a late touchdown but had his first three-interception game since losing a winner-take-all finale against Washington in 2012. "Just couple poor decisions that I made tonight."

KAEPERNICK CLICKED EARLY

It didn't take Kaepernick long to put that rough preseason behind him, leading the 49ers 80 yards in just three plays on their first possession. He stepped out of an ankle tackle by Jeremy Mincey and threw 29 yards on the run to Davis, who juggled the ball as the crossed the goal line before holding on for a 14-3 lead.

The 49ers also had an efficient drive in their 2-minute offense to finish the first half, with Kaepernick throwing for 39 yards leading to Carlos Hyde's 4-yard scoring run. Kaepernick was 16 of 23 for 201 yards without an interception.

SEA OF RED

When Romo wasn't throwing interceptions, the Dallas offense was getting false-start penalties and using timeouts to avoid delay-of-game penalties. Part of the problem was the noise from large swaths of red-clad 49ers fans seeing their team for the first time in the regular season in the $1.2 billion home of the Cowboys. "I noticed that," Harbaugh said of the crowd. "Much appreciated. Means a lot."

ON THE RUN

Murray bounced back from the fumble on his first carry of the season to get 71 yards in the first quarter and 118 with a touchdown for the game. The 49ers' Frank Gore had 63 yards, becoming the 29th NFL player with 10,000 for his career. He's also the 10th player with 10,000 yards and 10 seasons with the same team.

THE RECEIVING END

Davis, who had four catches for 44 yards, now has 53 receiving touchdowns, most of the NFL since 2009, playoffs included. Detroit WR Calvin Johnson, who plays Monday night, has 52. Anquan Boldin led all receivers with 99 yards. Bryant stayed down for several moments after Reid's interception return and later was treated for dehydration. He had four catches for 55 yards.

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