BALTIMORE (AP) — In case it wasn’t evident before opening day, we now know why the Baltimore Orioles added another slugger to a team that led the major leagues in home runs last season.

Nelson Cruz celebrated his Orioles debut by hitting a tiebreaking home run in the seventh inning, and Baltimore beat Jon Lester and the defending World Series champion Boston Red Sox 2-1 Monday.

Signed as a free agent in February, Cruz lined a solo shot into the left field seats to put the Orioles ahead. He hit 27 homers last year with Texas during a season marred by a 50-game suspension from Major League Baseball in the Biogenesis drug scandal.

Cruz joins a batting order that features Chris Davis, who led the majors in 2013 with 53 homers and 138 RBIs. Davis went 0 for 3 with two strikeouts as the cleanup hitter, but it didn’t matter because the guy in the 5-hole picked up the slack.

“It takes some of the pressure off everybody in the lineup knowing that you can pass the baton and the next guy can pick it up,” Davis said. “We have to know as hitters going into the game that we can be patient, we can wait for our pitch, knowing that the guy behind us can pick us up.”

Cruz, meanwhile, couldn’t have been more delighted. Not only did the Orioles provide him with a fresh start, but the fans chanted “Cruuuuuze!” every time his name was announced.

“It was really neat, it was special,” he said. “I made the right call to come and be part of this organization, be part of this town.”

Cruz wasn’t the only player to enjoy a successful start with his new team.

After missing two seasons recovering from knee surgery, Boston center fielder Grady Sizemore marked his return from a 922-day absence with a second-inning single for his first hit since September 2011. The three-time All-Star for Cleveland later hit his first home run since July 15, 2011, which also came at Camden Yards.

“Today was very exciting,” Sizemore said. “I couldn’t wait to get to the ballpark.”

Zach Britton (1-0) got the win with two scoreless innings of relief and Tommy Hunter got three outs for the save. Hunter earned the job as closer this spring after the Orioles dealt away Jim Johnson during the offseason.

The Red Sox got two on with one out in the ninth before World Series MVP David Ortiz hit a flyball and Jackie Bradley Jr. took a called third strike.

“It’s life in baseball,” Hunter said. “You’ve got to earn everything you get. One-run game to start the season off against the defending world champs.”

Starting on the road for the fourth year in a row, the Red Sox got nine hits but stranded 12 and went 0 for 10 with runners in scoring position.

“We had a lot of opportunities, we had a lot of guys on,” second baseman Dustin Pedroia said. “We just hit the ball right at people. It was one of those deals where we couldn’t find a way to push runs across.”

Making his fourth straight opening day start for Boston, Lester (0-1) gave up two runs, six hits and a walk in seven innings. He struck out eight.

Orioles starter Chris Tillman allowed one run, seven hits and a walk in five innings. The right-hander went 3-1 against Boston last year, but in this one he needed 104 pitches to get 15 outs.

Britton gave up a one-out double to Xander Bogaerts in the sixth and got three straight outs in the seventh, the only time all day that Boston went down in order.

Evan Meek walked two in the eighth before Brian Matusz retired A.J. Pierzynski on a comebacker.

Gametime temperature was announced at 60 degrees, but a stiff wind chilled many in the crowd of 46,685 — the 23rd consecutive opening day sellout at Camden Yards.

Hopeful that the offseason acquisitions of Cruz and right-hander Ubaldo Jimenez will enable Baltimore to return to the playoffs after missing out last year, Orioles fans were out in force. Until recently, games against Boston often drew as many Red Sox backers as those rooting for the home team.

“Our crowd was legit,” Hunter said. “That was awesome. I hope they come out like that every game for 80 more here.”

The Orioles used a walk, a single by Matt Wieters and a double-play grounder to take a 1-0 lead in the second.

The Red Sox put runners at second and third with two outs in the third before Tillman struck out Mike Carp. In the fourth, Sizemore hit a 3-1 pitch over the right-field wall.

NOTES: Dustin Pedroia got Boston’s first hit of the season, a one-out single in the first inning, to extend his hitting streak on opening day to eight games. … After taking Tuesday off, the teams meet Wednesday night. John Lackey (13-5 lifetime against Baltimore) faces Jimenez in his Orioles debut. … The Red Sox put RF Shane Victorino (hamstring) on the 15-day disabled list and recalled Bradley. … Ortiz received his 12th opening day start at DH, tying Don Baylor’s major league record at the position.

Jackie Bradley Jr. was recalled from Triple-A Pawtucket and Daniel Nava started in right field against the Orioles.

Manager John Farrell said Victorino has a Grade 1 strain.

“It’s going to require some time down,” Farrell said. “Whether that is 15 days or beyond, remains to be seen.”

“As we tapped into our depth last year many times over, unfortunately we’re doing it on Day One,” he said.

Victorino was hurt while running the bases Saturday in Boston’s final exhibition game. The move is retroactive to Sunday, the day an MRI revealed the strain.

The 33-year-old Victorino won a Gold Glove last season and hit .294 with 15 home runs, 61 RBIs and 21 stolen bases. He also got the big hit that helped Boston break open the clinching Game 6 of the World Series against St. Louis.

“He’s done such a great job for us,” Farrell said. “You’re talking about a Gold Glove guy at the top of the order.”

Victorino has had trouble with injuries. He was on the disabled list last year with a strained left hamstring and played only 10 games in spring training following right thumb surgery in December.

Bradley hit .189 in 37 games last season.

“With Vic out of the lineup we’re going to see a little bit of a rotation with all five of those outfielders,” Farrell said. “That’s kind of where we are.”