BALTIMORE -- The Baltimore Ravens got back to their roots against the Buffalo Bills in the regular-season opener on Sunday.

The Ravens used a swarming defense and a couple of opportunistic plays by quarterback Joe Flacco to escape with a 13-7 victory. It was a formula reminiscent of Baltimore's Super Bowl winning teams in 2000 and 2012.

"It was an excellent team victory," Ravens coach John Harbaugh said. "I thought our guys figured out how to play winning football throughout the course of the game. We've played these guys a few times now and it has been like this every single time. It has been right down to the wire."

Flacco was playing in his first regular-season game since Nov. 22 when he tore both his ACL and MCL in his left knee against the then-St. Louis Rams. That surgically repaired left knee was tested often on Sunday as Flacco dealt with constant pressure and was sacked four times.

He completed 23 of 34 passes for 258 yards with a touchdown (99.9 rating).

Newly signed wide receiver Mike Wallace caught three passes for 91 yards, including a 66-yard touchdown that provided a 10-0 lead in the second quarter.

"It feels good," Flacco said about the knee. "I think it held up well. I had some hits around my legs and some hits up top. I was really happy with how it felt."

The Bills led the league in rushing last season, but managed just 65 yards on the ground. Buffalo was also hampered by mistakes, and committed eight penalties for 89 yards.

The offense for both teams sputtered in the second half. A 37-yard field goal by Justin Tucker gave Baltimore a 13-7 lead with 5:30 left in the fourth quarter. Buffalo had another key holding penalty on the next possession that forced a punt and never got the ball back as the Ravens held on for the win.

"It's a pretty darn good defense over there," said Bills coach Rex Ryan, who instilled a lot of that attitude when he was the defensive coordinator in Baltimore. "I'm probably one of the only coaches that'll give credit to the opponent because they deserve it. That defense played extremely well. They're well coached and they got after us."

Bills quarterback Tyrod Taylor took several jarring hits from the Ravens' aggressive pass rush and was sacked twice. He completed just 15 of 22 passes for 111 yards. Running back LeSean McCoy was held to just 58 yards on 16 carries.

"It's game one," McCoy said. "The goal wasn't to be undefeated. The goal is to win our division. We'll come out next week ready to roll."

The Bills managed just two yards of offense in the opening quarter and trailed 3-0 after Tucker hit a 50-yard field goal.

The Ravens extended the lead with 10:11 left in the half when Wallace ran past safety Duke Williams and caught a pass in stride from Flacco for the 66-yard score on a third-and-1 play.

"This felt so right," Wallace said. "It's been so natural since the first day I got here."

Buffalo pulled to within 10-7 on a one-yard run by McCoy on fourth down. That touchdown was set up when Taylor escaped a sack with a spin move and found tight end Charles Clay for a 33-yard gain.

But that was all the Bills' offense could muster on a frustrating afternoon and there isn't much time to correct those mistakes with a Thursday night game looming against the New York Jets.

"We have to be better," Taylor said. "We have a quick turnaround, and we'll be ready to perform next Thursday night."

NOTES: Bills OLB Jerry Hughes posted an Instagram video of himself with fellow LB Zach Brown travelling via Uber to M&T Bank Stadium after they missed the first team bus. Both players were active for the game. ... LT Ronnie Stanley and LG Alex Lewis were in the starting lineup for the Ravens, who became the first team since the 1995 Carolina Panthers to start a pair of rookies at those spots in a season opener. ... Bills WR Sammy Watkins, the fourth overall pick in 2014, was in the lineup after undergoing offseason foot surgery. ... Ravens RB Buck Allen, a second round pick last year, was a healthy scratch. ... Bills starting LT Cordy Glenn injured his ankle in the second quarter and did not return.