SAN FRANCISCO — Even after watching the 49ers hang on for a 17-16 victory over the Denver Broncos in their exhibition opener Friday night at Candlestick Park, coach Mike Singletary was less than impressed.

“Thank God for preseason,” he said.
There wasn’t much of a pass rush. Neither quarterback dazzled. The biggest offensive star was a third-string fullback named Brit Miller, who scored two touchdowns and who prompted this question during Singletary’s postgame news conference: “Who is Brit Miller?”
The secondary, however, left very little to complain about. The 49ers had three interceptions, and Reggie Smith snatched away a Chris Simms pass on a two-point conversion attempt in the final minutes to save the game.
For a night at least, the defensive prowess overshadowed the quarterback debate. But for the record, Shaun Hill went 2-for-2 for 41 yards. Alex Smith followed up by going 5-for-7 for 33 yards, including a 3-yard touchdown pass to Miller.
“I thought they played OK,” Singletary said of the quarterbacks.
“Nothing to really make you jump one way or the other.”
Instead, it was the defense that stole the show — and the ball.
Nobody was happier about it than Dre’ Bly, who was waived by the Broncos in February. He described his final year in Denver as “miserable” and questioned the way coaches used him. Bly thought the Broncos had him play too conservatively and wasted his big-play potential.
And Friday, wearing the 49ers’ new throwback uniforms, Bly showed them what they missed.
The cornerback snatched away a Kyle Orton pass intended for Brandon Stokley at the 49ers 26-yard line. Bly celebrated as if it were January, not August.
“It’s like a rivalry, a fun rivalry,” Bly said.
It was a big moment for Bly beyond sentimental reasons. He is competing against Tarell Brown for the starting right cornerback job.
Brown sat out because of a toe injury. He was joined on the sideline by healthy starters. Running back Frank Gore, receiver Isaac Bruce and linebacker Patrick Willis had the night off because Singletary wants to keep them fresh for the regular season.
Veteran cornerback Nate Clements was on the field, though, and set the tone for the night with the 49ers’ first interception.
On second-and-goal from the 3, Orton tried to squeeze the ball to tight end Daniel Graham. But the ball sailed wayward and into the arms of Clements, who grabbed the interception in the end zone.
“I think that guys were just relaxed out there, taking chances, trusting and believing in what they saw,” Clements said of the defense.
Smith capped the interception parade by cutting in front of Jabar Gaffney on yet another ill-advised pass from Orton. Smith, a third-round pick a year ago, played three games without a start as a rookie.
“I’m just trying to show what I can do,” he said.
On offense, running back Glen Coffee, filling in for Gore, rushed 14 times for 67 yards.
That was nothing compared with Miller, who caught a 3-yard touchdown pass from Smith in the first half and a 40-yard touchdown pass from Damon Huard in the fourth quarter.
Miller, who started his career as a linebacker but is trying to catch on as a fullback, had two catches for 43 yards and two touchdowns. After the game, a TV camera crew approached for an interview. “Sure,” Miller said. “But I’ve never done this before.” In the locker room later, Miller said that running backs coach Tom Rathman recently gave him good advice.
“He told us, ’You only get so many opportunities in life, and even fewer in football,”’ he said.
The 49ers suffered two significant injuries. Fullback Zak Keasey suffered what is believed to be a forearm fracture in the first quarter.
He will undergo further tests on Saturday before a timetable is set for his return.
Thomas Clayton, one of the NFL’s leading preseason rushers the past two seasons, suffered a right knee sprain with 10:25 remaining in the game. He was taken off the field on a cart after being surrounded for several minutes by concerned teammates.