Hunter Pence was a key offseason pickup for the Phillies as they try to defend their NL East crown. (Kathy Willens/AP)

The last the world saw of the Philadelphia Phillies, they were skulking off the field at a hushed Citizens Bank Park, having just succumbed to the St. Louis Cardinals in Game 5 of the National League Division Series. Well, that was true of all but one of the Phillies. As his teammates vanished, slugger Ryan Howard, sprawled out near the first base line, was writhing in pain and grabbing his left foot.

As the Phillies prepare for another title defense, they do so with the knowledge that little has gone right for them since that final image from 2011. Nearly six months later, Howard’s torn Achilles’ tendon remains the perfect metaphor for the Phillies: The champs have fallen, and they can’t get up.

“We’re the team to beat until somebody beats us,” Manager Charlie Manuel told reporters Sunday in Florida, as the Phillies prepared to break camp and head north. “We ain’t gonna lay down and die.”

That Manuel felt the need to make such an empty show of bravado in the first place speaks to the perilous position the Phillies are in — and the degree to which they understand it. With their season set to open Thursday at Pittsburgh, the Phillies’ half-decade hold on the NL East crown has never appeared more tenuous.

The Phillies’ own acute health issues and the offseason improvements of some key NL East rivals has – at least on paper — reduced the gap between the champs and the rest of the division. In 2011, the Phillies, with a $160 million payroll, coasted to the division title, winning an MLB-best 102 games and topping the second-place Atlanta Braves by 13 games. But they failed to get out of the first round of the playoffs, losing in Game 5 to the Cardinals, 1-0, when ace Roy Halladay was outpitched by Chris Carpenter.

The Phillies’ lineup that day had Chase Utley in the No. 2 spot and Howard batting cleanup. But when the Phillies open the 2012 season, neither superstar will be in the lineup. Howard is expected to remain out until at least June, while Utley, battling chronic knee injuries, may not return until May. And in the case of Utley, there is some question as to whether he can ever again be the perennial all-star he was at the end of the last decade, when he averaged 29 homers and 101 RBI from 2005 to ’09.

“We’ve always been very good at being able to sustain our production through injuries,” assistant general manager Scott Proefrock said. “Our depth has been good enough, and the rest of our talent good enough to persevere. We’re hoping we’re in the same position this year.

“The only guy we haven’t had to go without for any extended period of time is the first baseman [Howard]. You look back, and he’s been the one constant through all that. That’s part of what has made him so valuable.”

The Phillies – whose only significant offseason move was replacing Ryan Madson as closer with free agent Jonathan Papelbon — are about to see exactly how far three aces can carry them. More than ever, the all-star trio of Halladay, Cliff Lee and Cole Hamels at the front of the rotation is going to have to cover up a lot of flaws – which they are certainly capable of doing. Together, they went 50-23 with a 2.51 ERA in 2011, and each made the NL all-star team.

But the Phillies’ offensive engine, which has been leaking runs for a few years now (from a peak of 892 runs in 2007 to a 10-year low of 713 in 2011), may struggle just to be league-average this year. Without Utley and Howard, it will be a patchwork lineup, with longtime leadoff man Jimmy Rollins (at least for now) sliding down to the third spot, and Hunter Pence, a key midseason pickup in 2010, batting cleanup.

Second base will be manned by 22-year-old rookie Freddy Galvis, a converted shortstop with a slick glove but a career OPS of just .613 in the minors, while first base will be split among veterans Jim Thome and Ty Wiggington and 28-year-oldJohn Mayberry Jr.

“We still have a good team. It’s not the same, by any means, but I’m not discounting our chances,” Rollins said solemnly on March 19, the day Utley left camp to see a specialist about his knees. “It’s going to be different. We didn’t have a great team in ’07 and we didn’t have a great team in ’08, but we found ways to win. We’re kind of back there.

“We’re going to have to find a way to execute, [place an] urgency on winning. Those things are going to be more important because we have lost a lot of pop.”

As the Phillies well know, their task is made tougher by the improvement below them in the NL East. While the Braves mostly stood pat, following a gruesome collapse that left them one win shy of a playoff berth, both the Miami Marlins and Washington Nationals made significant upgrades over the winter. The Marlins spent nearly $200 million on free agents ahead of their move into a gleaming new stadium, while the Nationals, who added all-star lefty Gio Gonzalez, are widely viewed as a rising power in the East.

“There’s no question the whole division got better,” Lee said. “Just look at the additions the Marlins made, and the way the Nationals are coming together. We’re focused on ourselves, doing whatever we can to get better, but you can’t deny what’s gone on in our division.”

Should the Phillies fail in 2012, it will inevitably prompt questions as to whether the championship window for this core group – the one largely responsible for these five straight division titles and the 2008 World Series championship — has slammed shut. Hamels will be a free agent after the season. Utley and Rollins will be 34 by next opening day. Howard will be 33.

Perhaps it will never come to that. Their history and track records say the Phillies should get the benefit of the doubt, until proven otherwise.

But as the Phillies surely understand, if the talent gap between themselves and the rest of the division was still as obvious and acute, such a thing would never have to be stated explicitly.