The Super Bowl champion New England Patriots of 2003 and 2004 were the best big-game team in the history of football.

Those teams consistently out-toughed the top teams in the NFL, both physically and mentally. The result was a pair of Super Bowl titles that came against seemingly insurmountable scheduling odds.

Patriots fans this year, meanwhile, have called into question the team's mental toughness after three losses by a total of four-points, including Sunday's excruciating 24-23 defeat at Seattle.

Those close losses against tough teams represent a startling contrast with the record-setting big-game proficiency of the Super Bowl champion Patriots of a decade ago. They make it reasonable to wonder if the team has in fact lost its mental edge, once its greatest attribute.

The Best Big-Game Team in History

The Cold, Hard Football Facts do not throw around accolades like "best big-game team in history" lightly. Hell, if you've seen us in action at our tailgates, you know we do very little lightly. Heavy is our middle name.

And we bring a heavy dose of data to support our claims.

We base our claim on a consistent ability to beat the NFL's best teams.

!The 2004 Patriots went an incredible 10-1 against what we call Quality Opponents (7-1 in the regular season) – that is, against teams with winning records.

Only one team in history was better against tough competition: the 2003 Patriots! They went an amazing 10-0 against Quality Opponents.

It's a truly stunning and unmatched feat of big-game excellence. The Patriots went 34-4 overall in 2003 and 2004, a record number of wins over a two-game span. They won a record 21 games in a row along the way.

But the most remarkable aspect of that record-setting performance is that they went 20-1 against Quality Opponents. A slate that includes 21 of 34 games against teams with winning records almost always spells failure in the highly competitive NFL.

No team before or since has come close to matching that ability to consistently beat playoff contenders. It just stands to reason that it's tough to consistently beat good teams in the NFL.

In fact, only one other team in the history of football beat 10 Quality Opponents in a single season: the dynastic 1979 Steelers went 10-3 against teams with winning records, ending the season with their fourth Super Bowl victory in six years.

The Patriots, meanwhile, topped 10 Quality Opponents twice in two years. Here's the short list of the only clubs in history to beat 10 Quality Teams in a single season.

• 2003 Patriots – 10-0
• 2004 Patriots – 10-1
• 1979 Steelers – 10-3
  For a little perspective, the undefeated Dolphins of 1972 went 2-0 against Quality Opponents before adding three more wins in the postseason (great team soft schedule = only undefeated team). The 18-1 Patriots of 2007 fell just short of the record set by the 2003 team, with a 9-1 record against Quality Opponents.

The Patriots reached their big-game zenith in the 2004 postseason, embarrassing Peyton Manning and the Colts, 20-3, in the divisional playoffs after a year in which Indy scored 522 points, wiping out the 15-1 Steelers and the NFL's No. 1 defense, 41-27, at Pittsburgh in the AFC title game and then edging out Philadelphia, 24-21, in Super Bowl XXXIX.

It pays to remember those Eagles were a dominant 13-1 team before resting their starters for the final two regular-season games.

By the way, no team in NFL history has overcome a tougher postseason slate than the 2004 Patriots to win it all. New England's playoff opponents that year were a combined 40-8 (.833) in the regular season.

The Patriots proved they could beat great offenses with defense and great defenses with offense. It was brilliant football against elite teams.

The Loss of Mental Toughness

Fast forward to more recent years and it has become apparent that the Patriots simply do not have that edge, whether mental or physical, to tough out wins against quality competition.

The Patriots are 0-3 against Quality Teams this year, losing to all three teams they've faced with winning records (Arizona, Baltimore, Seattle) – and losing all three in excruciating fashion.

The Patriots blew last-minute leads to both the Ravens and Seahawks, and missed a late field goal that would have topped the Cardinals. In all three cases, those losses can be seen as a loss of that mental edge. The Patriots no longer strangle the life out of tough opponents in tight games.

But the struggles go back even further.

The 2011 Patriots faced just two Quality Opponents during the regular season, a very soft schedule compared to the champion teams of 2003 and 2004.

The Patriots lost both those games, too.

New England went 15-4 last year including the postseason, with its only Quality Win in the AFC title game against Baltimore. Even the most ardent Patriots fans will admit the team survived the Ravens more than they beat them.

The Patriots last beat a Quality Opponent in the regular season way back in Week 15 of 2010, when they held on for a 31-27 victory over back-up Matt Flynn and the Green Bay Packers.

They are 1-6 against Quality Opponents since then, benefitting last year largely from a soft schedule – just four Quality Teams (1-3) in 19 games including playoffs – and now 0-3 against Quality Opponents this year.

There are other issues to consider this year. Namely, the Patriots are on pace to field the worst pass defense in franchise history and one of the worst of all time, with a 100.9 Defensive Passer Rating.

But even when they do compete against tough teams, they're no longer winning. It's easy to point the figure at a failure of mental toughness – the team's hallmark in its Super Bowl glory days.