New York ? With less than a month to go before opening day, baseball at last decided who’s in and who’s out come October. Now, even a third-place team can win the World Series.

Major League Baseball made it official Friday, expanding the playoff format to 10 teams by adding a wild-card club to each league.

“I hope we get that extra spot,” said new Houston Astros general manager Jeff Luhnow, whose team is coming off a 56-106 finish that was the worst in the majors. “I think it’s great any time you have more markets involved.”

Boston and Atlanta sure could’ve used this setup last year. They went through awful collapses in September that eventually cost them playoff spots on the final day of the season.

“I think the more, the merrier,” new Red Sox manager Bobby Valentine said. “I think for the fans, the players, the energy at the end of the season, I don’t mind. What would it be, a third of the teams? I think it’ll be good.”

This is the first switch in MLB’s postseason format since the 1995 season, when wild cards were first added. The move creates a new one-game, wild-card round in the AL and NL between the teams with the best records who are not division winners.

The additions mean 10 of the 30 MLB teams will get into the playoffs. That’s still fewer than in the other pro leagues — 12 of 32 make it in the NFL, and 16 of 30 advance in the NBA and NHL.

The long-expected decision was announced less than an hour before Seattle and Oakland started the exhibition season. On March 28, the Mariners and Athletics will play the big-league opener in Tokyo.

“This change increases the rewards of a division championship and allows two additional markets to experience playoff baseball each year,” Commissioner Bud Selig said in a statement.

Also, a tweak: For the 2012 postseason, the five-game division series will begin with two home games for lower seeds, followed by home games for the higher seed. After that, it will return to the 2-2-1 format previously used. If the World Series goes to Game 7 this year — as it did last season, when the wild-card St. Louis Cardinals won the championship — it would be played Nov. 1.