ORCHARD PARK - To be clear, when Donte Whitner made his provocative guarantee that the Buffalo Bills were going to make the playoffs this season, the safety didn't mention anything about finishing with a perfect record.

So when the Bills entered their bye this week coming off their first loss - and a dreadful one at that at Arizona - Whitner wasn't left entirely dejected.

“It's been a while since we lost, but nobody's down,” Whitner said. “We're not discouraged at all.”

What's important to keep in perspective is that the Bills (4-1) are still off to their best start in 16 years, sitting atop the AFC East in a race that's suddenly wide open now that the perennially dominating New England Patriots have fallen back to the pack after losing Tom Brady to injury.

If this year is about the Bills proving that they are, in fact, for real, the next test in their maturation is discovering what they're made of by showing how they respond to adversity

It starts with Buffalo hosting San Diego on Oct. 19, followed by three straight games against division rivals, a stretch which will begin determining how the East shakes out and whether Buffalo is capable of ending an eight-season playoff drought, the longest in franchise history.

As well as the team played in winning its first four games, three of them sparked by fourth-quarter comebacks, there were cracks that began to show in how Buffalo thoroughly unraveled in a 41-17 loss to the Cardinals.

It was a sloppy, Murphy's Law-type of game in which anything and everything went wrong: from quarterback Trent Edwards being knocked cold by a concussion on the third play from scrimmage to backup J.P. Losman committing three turnovers, and a once-stout defense that had absolutely no answer to Kurt Warner's ultra-efficient quick-pass attack.

The offense has numerous concerns that require addressing, starting with Edwards' health. The second-year player, who won the Bills starting job midway through last season, did not practice this week to allow him time to recover from post-concussion symptoms.

The 2007 third-round draft pick out of Stanford has been credited for playing a key role in Buffalo's overall resurgence and providing a spark to what had formerly been a sputtering offense. He's gone 81-of-122 for 948 yards with four touchdowns and two interceptions.