Bryce Harper bowed to his new fans, Mookie Betts and the Boston Red Sox began the defense of their World Series crown and the great Mariano Rivera threw one more strike from the mound at Yankee Stadium.

Then, in ballparks across the land, it was time to begin on a homer-filled opening day.

Lorenzo Cain made the big catch. Javier Baez swung a powerful bat. And Jordan Zimmermann came close to giving Major League Baseball a perfect start Thursday.

A week after Ichiro Suzuki and the Seattle Mariners swept two games from Oakland at the Tokyo Dome, everyone was in action. In many places, the ball was flying — at Dodger Stadium, Los Angeles set an opening day record by hitting eight home runs.

The packed crowd at Citizens Bank Park was especially energized by Harper and the Philadelphia Phillies in a 10-4 win over Atlanta.

“The atmosphere was unbelievable,” Harper said. “The atmosphere was rocking all through the game.”

A year after the conditions were more fit for snowballs than baseballs at some stadiums, the weather was fine. A little rainy in Kansas City, causing a slight delay, but no freezing temperatures anywhere.

Cy Young Award winners past and present took the hill — Jacob deGrom and Max Scherzer delivered the marquee matchup that was expected, but a duel never developed between Justin Verlander and Blake Snell. Zimmermann carried a perfect game into the seventh inning for the Tigers at Toronto.

Robinson Cano, Andrew McCutchen and Marwin Gonzalez got key hits for their new clubs, but Harper, Manny Machado and Paul Goldschmidt didn’t.

Fernando Tatis Jr. represented the rookies well — just a few months past his 20th birthday, the highly touted San Diego Padres prospect became the youngest player with a multihit game in an opener since Robin Yount in 1975.

Playing up the power factor that often dominates these days, the NL champion Dodgers tied a franchise record for home runs and romped past Arizona 12-5.

“Everyone kind of knocked us last year for scoring too many runs off homers,” said Max Muncy, who also connected. “But if you’re going to do it, you might as well do it like that.”

New managers began with a mixed bag. Minnesota’s Rocco Baldelli and Cincinnati’s David Bell won while Brandon Hyde, taking over the 115-loss Orioles, Toronto’s Charlie Montoyo, Texas’ Chris Woodward and the Angels’ Brad Ausmus lost.

“I think the dugout seemed a little quieter than normal,” Hyde said. “I just felt like it was quieter than normal because of some jitters from some younger players.”

The sellout crowd in the Bronx had plenty to cheer, including Rivera’s ceremonial first ball. The first player to be unanimously elected to the Hall of Fame, he zinged it, too.