SANTA CLARA, Calif. — It was like a slow bleed for the Giants’ defense.
Eventually the series of paper cuts became a bloody mess.
One by one, on every key 49ers drive in the Giants’ 30-12 loss on Thursday night at Levi’s Stadium, San Francisco was killing them on third down.
It began on the 49ers’ opening drive and continued all night.
The 49ers offense went 7-for-10 on third downs in the first half to keep scoring drives alive as they took a 17-3 lead.
They finished the game a more modest 9-for-16 for 56.3 percent, but the damage was done much earlier.
Similar damage happened when the Giants were on offense.
They converted just three of 12 third downs, which heavily contributed to the 49ers controlling the ball for 39:10 to just 20:50 for the Giants.
“On both sides, third down was a huge [factor] in this game,’’ Giants head coach Brian Daboll said afterward. “It was a contributing factor to [San Francisco having nearly double the] time of possession. When you’re not converting third downs and you’re giving up some third downs, there’s time of possession [problems]. The defense gets tired and we’re not on the field offensively enough. So, it was a collective thing.
Daboll said that when San Francisco went 7-for-10 in the first half, “a few of them were screens where they just caught and ran. We’ve got to rally to the ball and make tackles.’’
The Giants tackling, as it was in their 31-28 win at Arizona on Sunday, was atrocious.
They could not stop 49ers running back Christian McCaffrey, who had 85 rushing yards on 18 carries, or receiver Deebo Samuel, who caught six passes for 129 yards, many of which came after first contact.
“Obviously, we need to put more emphasis on tackling,’’ Giants linebacker Bobby Okereke said. “We have a lot of missed tackles across the board at different positions. Execution-wise, guys just have to do their job, starting with me.’’
On the 49ers’ first offensive possession, Brock Purdy passed to Samuel for 14 yards on third-and-6.
Then it was Purdy to Jauan Jennings for 24 yards on third-and-8.
The 49ers got a field goal out of that series.
On the 49ers third possession, which produced their first TD and a 10-3 lead, they kept a drive alive with a 30-yard catch-and-run by Samuel and then a 17-yard pass play to McCaffrey on third-and-13.
They made it 10-3 on a scoring pass to Ronnie Bell on third-and-goal from the 9-yard line.
When the 49ers took a 17-3 lead, the key play was a 12-yard pass play from Purdy to George Kittle and penalty yardage tacked when Leonard Williams was called for roughing the passer.
“I don’t know what the conversion rate was, but obviously it was bad,’’ cornerback Adoree’ Jackson said.
“We’ve got to tighten up third down,’’ safety Jason Pinnock said. “We’ve got to tackle better. It’s got to be an emphasis.’’
“They beat us on a lot of third downs,’’ defensive lineman Dexter Lawrence said. “We got them in some third-and-long and they were converting. We’ve got to be better in those situations. They were just making plays. We know we’ve just got to be better. We’ve all got to run to the ball.’’
