In the big leagues, there isn't much of a difference between a September to remember followed by October glory and five months of contention disappearing as quickly as those hot August nights.

In some cases it could be a key injury, a poorly timed slump by a cleanup hitter, a streak of bizarre one-run losses or a few bullpen blowups that tell the tale. More often than not, late-season fades ultimately reveal deficiencies that were there all along but simply disguised by excellence in other areas when the pennant races weren't revving up to full tilt.

This offseason, clubs that came close in 2009 attempted to deal with these areas of weakness by fortifying them with new blood and a new attitude. Time will tell how things will shake out, but one thing's for sure: The biggest changes have to come from the top, and the most important players are not always, well, players.

Following is a look at five coaches who could make a huge difference in 2010.

Rick Peterson, pitching coach, Milwaukee Brewers
Peterson, 55, has 11 years as a big league pitching coach under his belt, most famously in his 1998-to-2003 stint with the Oakland A's that had him mentoring Barry Zito, Mark Mulder and Tim Hudson, a.k.a. the "Big Three." He went to the Mets after that and has been a free agent since the end of the 2008 season.

But Peterson isn't just about changing pitchers -- he's about changing philosophies. And in that respect, the Brewers have bought into his psychology degree and biomechanical-analysis approach.

"I asked right up front: Are you looking just for a big league pitching coach, or are you looking for an organizational philosophy?" said Peterson, who is on board for two years. "I'm more interested in integrating a philosophy, and that's what they were looking for.

"When you look at my career path, my life's path, I tried to design the best pitching system that could be designed, and now I'm coming to an organization that embraces that."

After a 2009 season that saw the Brewers fade from contention in part because of a 4.83 team ERA that ranked next to last among the 16 National League clubs and a starters' ERA of 5.37, which tied with Baltimore for the worst mark of all 30 Major League clubs, the Brewers brought in lefties Randy Wolf and Doug Davis through free agency. Now Peterson will be tasked with making it all click.

Bobby Ramos, bullpen coach, Tampa Bay Rays
It might seem a bit strange to say that a bullpen coach can play a pivotal role in a club's postseason chances, but the 2008 American League champion Rays finished third in the AL East last year, and a lot of it had to do with a relief corps that began the season in fine form and collapsed down the stretch.

The bulk of a talented core is back, with lefties J.P. Howell and Randy Choate and righties Grant Balfour, Lance Cormier and Dan Wheeler returning, but the key to Ramos' success in getting this crew back to its ironclad reputation of '08 could be the offseason acquisition of closer Rafael Soriano.

Last year, Ramos -- who was the Angels' bullpen coach during that club's 2002 World Series championship season -- began the 162-game schedule with his old friend, veteran Troy Percival, running the show as the team's closer and bullpen leader. But Percival was brittle after back surgery and didn't last long in the role. The rest of the season became a mishmash of matchups for a unit in search of -- and never really finding -- an identity.

"I think it just comes down to not having a security blanket," Wheeler said. "A Troy Percival, with his track record, just coming out there to close the game and us knowing exactly what we're going to do, knowing that 'Hey, we're going to line up in the seventh or eighth inning,' I think we did a pretty decent job using matchups -- it's not an easy thing to do. But we had to play with the hand we were dealt."

So did Ramos, and having Soriano as his younger, more physically reliable go-to guy (Soriano had 27 saves, a 2.97 ERA and 102 strikeouts in 75 2/3 innings for Atlanta last year) should give him -- and the Rays -- just a bit more to lean on late in those important divisional games.

Hensley Meulens, hitting coach, San Francisco
No matter what language you're speaking (Meulens, a native of Curacao, speaks five, by the way), the man who's supposed to help take the Giants from a pitching-heavy 88-win team in 2009 to a more well-rounded playoff club in 2010 can't just be all talk in his first year on the job.

The former Yankees prospect nicknamed "Bam Bam," who did wonders with the Giants' Triple-A Fresno team, is now in charge of an offense that drew 392 walks, the fewest in the Majors. Giants hitters also compiled a .309 on-base percentage, which also trailed both leagues. The best Giant in the NL in terms of pitches seen per plate appearance? Aaron Rowand, with 3.47, a figure that ranked 69th.

With all of that pitching to keep games close and a few extra offensive pieces -- the Giants signed Mark DeRosa and Aubrey Huff and re-signed Bengie Molina -- to play with, Meulens says he'll be patient in trying to preach patience.

"Not everybody can be taught the same," Meulens said. "Psychology plays a big part in me trying to get in a guy's head and find out what works for him."

Fortunately for the Giants, they already know a lot about Meulens, who conducted tutorials for John Bowker, Travis Ishikawa, Nate Schierholtz and Minor League prospect Brett Pill in the indoor batting cage at AT&T Park in the first week after his hiring.

"We have a lot of work to do to better the offense," Meulens said. "It's better to get started now instead of waiting until Spring Training to work on some things."

Rudy Jaramillo, hitting coach, Chicago Cubs
The brand-new offensive mastermind tasked with getting the Cubs back to the postseason has big shoes to fill. Fortunately, he's been wearing pretty big shoes, himself, for quite a while now.

Jaramillo comes to the Windy City after a Major League-leading 15-year stint as hitting coach for the Texas Rangers, and he's garnered a serious reputation as one of the best in the business. Now, he has a new challenge, with the Cubs having ranked second in the Major Leagues in runs scored in 2008 but not coming close to that level in 2009. Chicago finished 10th in the NL in runs scored and next-to-last with a .241 average with runners in scoring position.

Jaramillo's first order of business might be trying to get Alfonso Soriano back to the level of success the slugging outfielder has enjoyed in the past. Soriano hit .241 last year with a career-low OBP of .301, but the two worked together when Soriano was a member of the Rangers in 2004 and 2005, and Soriano averaged 32 homers and more than 97 RBIs in those two seasons.

If Jaramillo can work his magic with the Cubs, they could make a serious dent in the NL Central, the division they won in 2008 and were picked to win in '09. Despite the lack of offense, the Cubs hung in the race until September and still finished the year with an 83-78 record that left them in second place, 7 1/2 games behind the St. Louis Cardinals.

Now they've got one of the game's true hitting gurus, and Jaramillo says he's ready to do his thing.

"I always put myself as a teacher first, a coach second," Jaramillo said. "I have passion working with these young men. I love to see talent get better. I'm just trying to help these kids learn themselves and try to help them get the most out of themselves so they can get to a different level."

Eddie Perez, bullpen coach*, Atlanta Braves
Note the asterisk next to Perez's title, and also note that Perez figures to be a a lot more than a bullpen coach for the Braves in 2010.

Though his bullpen work will be key to the young Braves' playoff hopes this year, more important to the franchise's present and future could be the fact that Perez is viewed as a top contender to replace legendary skipper Bobby Cox, who has announced that 2010 will be his final season.

That means that Perez can be instrumental in helping Cox with leadership, organizational duties and in dealing with ramped-up media intensity, since Cox's mere presence in the ballparks of the NL is sure to bring about "Farewell Tour" emotion and responsibilities.

Perez joined Atlanta's staff in 2007 after 11 big league seasons behind the plate, nine of which were spent in Atlanta. He studied the game in a cerebral way, having earned the right to be the great Greg Maddux's personal catcher. In his three seasons as a coach, he quickly built very good relationships with players and also managed two winters in his native Venezuela.

"When I was a player, I used to get in [teammates'] faces and talk trash," Perez said. "As a coach, you have to be careful, because you have to tell them why they made an error or tell them, 'This is what happened and how you fix it.' But you can't get in their faces. You can't do that anymore. They don't learn that way."

Sounds as though he's already halfway there.