Out of nowhere, the Houston Astros got a huge head start on October.

On a dizzying day that featured two dozen trades, the Astros pulled off the biggest and most startling deal, adding ace Zack Greinke to an imposing rotation already loaded with All-Stars Justin Verlander and Gerrit Cole.

Plenty of familiar names were on the go Wednesday — Shane Greene and Mark Melancon boosted the Braves' bullpen, with Scooter Gennett, Jesús Aguilar, Mike Leake and Tanner Roark among those also moving.

But it was the Astros' acquisition of Greinke from Arizona for four minor leaguers that quickly became the talk of baseball. The deal came right before the deadline for swapping players to still have them eligible for the postseason.

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"We had him high on our list and we didn't know this was even remotely possible and it really wasn't until the last 48 hours and really the last 24 hours that we started to get traction on something," Houston general manager Jeff Luhnow said.

The AL West leaders and 2017 World Series champions added two other pitchers, too, getting starter Aaron Sanchez and reliever Joe Biagini from Toronto.

"Houston made some big deals. They're really good. They were good before," Red Sox President of Baseball Operations Dave Dombrowski said.

A lot of contenders were busy.

The Chicago Cubs added Detroit's Nicholas Castellanos to their lineup, the Phillies got outfielder Corey Dickerson from Pittsburgh and the Washington Nationals acquired relievers Daniel Hudson, Roenis Elías and Hunter Strickland.

In most cases, major leaguers were swapped for minor leaguers.

"When it comes to trades, one thing I've learned is, just wait," Cubs manager Joe Maddon said. "You've got to wait until the very end and it plays itself out. The 11th hour is the most powerful hour there is. To get things done before that, it normally doesn't work to get what you want. There's the 11th hour at work."

"When it comes to trades, one thing I've learned is, just wait. You've got to wait until the very end and it plays itself out. The 11th hour is the most powerful hour there is. To get things done before that, it normally doesn't work to get what you want. There's the 11th hour at work." — Cubs manager Joe Maddon

Several players whose names swirled in the tradewinds stayed put.

Giants ace Madison Bumgarner, Mets starters Noah Syndergaard and Zack Wheeler and Pirates closer Felipe Vázquez remained in place. So did Mets closer Edwin Díaz and Texas starter Mike Minor.

"Nothing changed for me. I never expected to be somewhere else until that happened," Bumgarner said. "I just have a job to do and I'm going to do it. We're going to miss a few guys we got rid of. That's going to be tough."

Major League Baseball made July 31 a hard deadline this year for trades. Now, no deals can be made until after the World Series.

"This was a unique deadline, it felt," said Yankees general manager Brian Cashman, whose AL East-leading team didn't make any significant moves.

Pitchers Marcus Stroman, Andrew Cashner, Homer Bailey and Jason Vargas were among the players who were traded in recent weeks.

And on Tuesday night, the Cleveland Indians agreed to send pitcher Trevor Bauer to Cincinnati in a three-team swap that brought back outfielder Yasiel Puig. That trade became official Wednesday, setting off a full morning and afternoon of swaps.

Wheeler heard the speculation involving him.

"It's almost happened several times and never did. I'm happy to be here and I'm concentrating on producing and doing well here," he said. "It was all there for it to happen and just didn't. I was ready for it, especially with me being a free agent after the season."

Atlanta concentrated its effort on padding its bullpen.

A day after getting reliever Chris Martin from Texas, the Braves got Greene from Detroit and Melancon from the Giants.

"We engaged everything — position players, starting pitchers, the bullpen — right up until the end," general manager Alex Anthopoulos said. "At the end of the day, where we thought there were deals that made sense for us and what we had to give up and so on, the bullpen made the most sense. But we definitely tried some other areas. We just couldn't wind up with a deal that made sense to our organization."

The 30-year-old Greene has 22 saves and 1.18 ERA and was an All-Star this season. He's likely to take over the closer's role — Luke Jackson had been the latest to try it for the Braves, and was just 17 for 25 in save chances.

"They're excited, I'm excited," Greene said in Anaheim, where the Tigers played the Los Angeles Angels. "I'm starting a new chapter and going to a contender."

At Yankee Stadium, Greinke had been pulled after five innings because of a rain delay and was watching video of his start when manager Torey Lovullo interrupted — GM Mike Hazen wanted to break the news.

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Hazen said the trade was finished in a hurry, in the final 20 minutes before the 4 p.m. deadline. Soon, word reached Progressive Field in Cleveland, where Houston was preparing to play the Indians.

Cole said the Astros did "a lot of hooting and hollering" about "getting a Hall of Fame pitcher, a craftsman."

"We are just really shocked and ecstatic," Cole said.

The 35-year-old Greinke is 10-4 with a 2.90 ERA this season. The Astros now have four starters with ERAs in the top 15 in the majors this year — Verlander is fifth with a 2.73 ERA, Greinke is ninth, Cole is 11th at 2.94 and Wade Miley ranks 14th at 3.06. Verlander leads the AL in wins (14) and ERA, and Cole tops the majors with 212 strikeouts.

"If we stay healthy," Luhnow said, "this team is as good as any team I've ever seen."