In their 28-25 loss at Indianapolis, the problems began cascading as Jacksonville drove early in the fourth quarter down 21-14. On third-and-1 from the Colts’ 8, Jones-Drew picked up the first down, but Williams (who had already dropped a sure touchdown pass in the third quarter) was called for an unnecessary roughness after pushing linebacker Tyjaun Hagler after the whistle, setting up a first-and-10 from the 22 instead first-and-goal from the 7. A false start penalty then pushed the Jaguars back to the 29. Eventually, they would settle for a field goal instead a game-tying touchdown.

Down 28-17, Garrard threw his first interception of the season on a pass near the end zone. Then after the Jaguars having closed to 28-25, Del Rio suffered from a lack of boldness in his coaching that he’ll need going up against New England’s Bill Belichick, who is so good in part because he makes calls like your little brother does playing Madden — unpredictable and unreasonable. Del Rio, with 2:47 left, kicked off long rather than going for an onside kick. Peyton Manning, instead of handing the ball off like most quarterbacks, completed two passes against a Jacksonville defense overplaying the run to help ice the game.

In the Jack Del Rio era, the Colts are to the Jaguars as the Patriots are to the Colts — a barometer of whether they are ready for greatness.

Jacksonville is only 3-7 against its AFC South rival, including losses in five of their last six meetings, since Del Rio became coach in 2003.

That loss made it seem that perhaps Jacksonville, despite its greater maturity, is not mature enough.

The Pittsburgh game just about sent that same message — though with a twist at the end that said maybe the Jaguars had grown up. Jacksonville blew a 22-7 fourth-quarter lead by making the same kind of mental errors that kept them from winning in Indianapolis, including another fourth-quarter interception by Garrard to Anthony “No More Guarantees” Smith, who ran it back to the Jaguars’ 12 to set up a Pittsburgh touchdown. The Jaguars failed to pick up a first down on third-and-3 on the ensuing possession, setting up Pittsburgh’s only sustained drive of the day (its first touchdown came after a shanked punt) to tie the score at 22.

But the Jaguars followed with the kind of fourth-quarter drive they need to win in the playoffs. They passed only twice, and ran six times for 53 yards in a 73-yard drive that provided the winning points in a 29-22 victory.

Now Jacksonville will travel to Pittsburgh again next week to attempt to win their first playoff game since 1999. If the Jaguars show the smarts they exhibited most of the season — including late in that fourth quarter against the Steelers earlier — they will be a playoff force to be reckoned with, as likely to bounce the Patriots as anybody. But their margin for error is small — and it’s been by being on the right side of that small margin that the Jaguars are feared instead of fearful.

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