SANTA CLARA -– The 49ers' defense appeared to be in complete control through the first 25 minutes.
But it all fell apart shortly after referee Terry McAulay called 49ers' safety Jaquiski Tartt for unnecessary roughness on Dallas Cowboys quarterback Dak Prescott late in the second quarter.
The Cowboys built momentum at the end of the first half and rode it to a 24-17 victory over the 49ers on Sunday at Levi's Stadium.
On a third-and-6 play from the Dallas 49, rookie Ronald Blair and defensive back Chris Davis combined for an apparent sack. The 49ers led 14-0, and it appeared they would regain possession of the ball with more than four minutes remaining in the first half.
However, an unnecessary roughness penalty on Tartt provided the Cowboys with 15 yards and a first down. Three plays later, Prescott found Terrance Williams for a 20-yard touchdown pass.
"I think it changed the game," 49ers coach Chip Kelly said. "We got to do a better job of avoiding that. I really didn't see . . . he said he blew the whistle to stop the play. I don't think anybody heard a whistle. I know no one on our sideline heard the whistle. But if the referee makes a call, it's correct. That's the way it goes."
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Blair and Davis had Prescott wrapped up when Tartt came in and gave Prescott a shove from behind to knock him down.
Tartt said he had no idea the penalty was called on him until much later.
"I couldn't hear the whistle," Tartt said. "Everybody was still playing. Their linemen were still trying to block me, so I don't know. No one heard the whistle. We were just playing. The crowd was really into it and really loud.
"After the offense received the ball. The coaches told me that the penalty was on me."
After a 49ers three-and-out, followed by Bradley Pinion's 26-yard punt, the Cowboys regained control and scored the game-tying touchdown with :12 remaining in the first half on Prescott's 4-yard pass to Brice Butler.
