For the Giants, this weekend’s contest with the Dallas Cowboys is a de facto playoff game. If the Cowboys win, they’ll have a one game lead plus a tiebreaker advantage – essentially a two-game advantage – with just four games left on the schedule. That would very likely give the division title to Dallas and leave Big Blue battling for a wild-card spot in a game of musical chairs that appears to have four NFC teams scrambling for two seats.

More than mathematical realities will be tested on Sunday, however. Giants fans will find out whether Big Blue is just an average team or a genuine contender. In games against good teams, this team has consistently come up short: The Giants are 1-4 against teams with winning records, with only a lastminute 24-23 win over the Broncos in their favor.

In Foxboro, meanwhile, the Jets face a New England team that is more vulnerable than it’s been in years. Despite their struggles, though, the Patriots have a comfortable two-game lead in the AFC East. During the summer, Jets fans thought this game would be Gang Green’s chance finally to vanquish its biggest rival and stake a claim as the division’s best team. Instead, the Jets can only try to make the ride a bit bumpier for a team cruising toward its fourth division title in five seasons.

Here’s a closer look at this weekend’s matchups:

COWBOYS (7-4) AT GIANTS (7-4) 1 p.m., FOX

WHEN THE GIANTS HAVE THE BALL

When these teams met earlier this season, the Giants had been scoring an average of 34 points a game; the Cowboys held them to just 13 points.The aggressive Dallas defense destroyed the Giants’ offensive rhythm, forcing four turnovers and sacking Eli Manning four times.

The Cowboys love to blitz and they can bring pressure from anywhere; defensive end Greg Ellis leads the team with eight sacks. Strong safety Roy Williams and cornerbacks Terrence Newman and Anthony Henry provide excellent man coverage. Sometimes the Cowboys will leave those defenders one-on-one while sending everyone else after the quarterback.

The Giants will need to counter by running quick passing routes and taking advantage of the mismatches between big receivers like Plaxico Burress and Jeremy Shockey and the smaller players in the Dallas secondary. They can also try to exploit the Cowboys’ aggressiveness with draw plays and screen passes.Tiki Barber should be able to break a couple of big plays if the Giants’ playcalling follows this strategy.

WHEN THE COWBOYS HAVE THE BALL

The Dallas offense is a strange beast. The Cowboys run the ball a lot, but they aren’t very good at it; they managed just 85 yards in their overtime loss to Denver on Thanksgiving, and a season-low 58 against the Eagles two weeks earlier. Julius Jones and Marion Barber both seem to be quality backs, but the offensive line has not done a good job of creating holes. While the Cowboys rank second in the NFL with 379 rushing attempts this year, their average of 3.4 yards per attempt ranks 28th.

So why do they keep running? Head coach Bill Parcells has made it clear that controlling the clock is his primary objective, and his team leads the NFL in time of possession. That’s important because the Cowboys have played a lot of close contests: Eight of their 11 games have been decided by six points or less, and sometimes the best way to keep your opponent from scoring is to hold on to the ball.

Drew Bledsoe has passed effectively this season because the line has given him more time to throw the ball than he ever had in Buffalo.Veteran receiver Keyshawn Johnson is Bledsoe’s favorite target, and Terry Glenn is still a dangerous deep threat. Jason Witten has also emerged as one of the better passcatching tight ends in the NFC.

But despite that range of weapons,Bledsoe remains one of the league’s least mobile quarterbacks. The Giants have a great pass rush, and they’ll need to get into the backfield and pressure the Patriots quarterback. Throughout his career, Bledsoe has struggled to deal with the pass rush. Michael Strahan and Osi Umenyiora can force him into making mistakes even if they can’t sack him.

KEY TO THE GAME

The Giants need to cut down on their mistakes. They are the third most penalized team in the league, and last week’s loss to the Seahawks illustrated just how costly mental errors can be. They Giants will never score enough points to beat the Cowboys if they’re constantly getting flagged for false starts.

Lahman’s Pick: Giants 21-17

JETS (2-9) AT PATRIOTS (6-5) 4:15 p.m., CBS

WHEN THE JETS HAVE THE BALL

The Patriots have won some close games this year, but their defense has struggled against potent offenses. Five of their six wins have come by a touchdown or less, and they were routed at home by both Indianapolis and San Diego.

Injuries have slowed Bill Belichick’s once dominant defense, but the biggest difference is that the Pats aren’t forcing turnovers like they used to. They rank near the bottom of the league in takeaways, and as result they’ve allowed 25.4 points a game, 26th in the NFL. The return of inside linebacker Tedy Bruschi in October gave the team an emotional boost, but it wasn’t enough to overcome the team’s problems on defense.

Another issue has been the lack of a consistent pass rush. Willie McGinest and Rosevelt Colvin are tied for the team lead with just 3.5 sacks.The Pats’ inability to pressure opposing quarterbacks has exposed a weak secondary.The Patriots have surrendered 21 touchdown passes while managing just five interceptions.

The Jets’ offense showed a few faint signs of life in a two-point loss to the Saints last week. Brooks Bollinger had his best game yet, passing for 251 yards and a touchdown. Curtis Martin rushed for 91 yards, his second-most productive day of the season. The Jets needs a repeat of both of those performances if they’re to upset the Patriots.

WHEN THE PATRIOTS HAVE THE BALL

One thing that’s been overshadowed by the Patriots’ struggles this season is that Tom Brady is having the best year of his career. He leads the NFL with 3,030 passing yards and continues to spread the ball out to a variety of receivers.

Ten different players have caught touchdown passes, which poses a serious challenge for opposing defenses. The Jets can’t just focus on one receiver, and will have to be prepared for any one of them to catch a pass in any situation.

New England’s ground game, on the other hand, has been slowed by injuries. Running back Corey Dillon has missed the last three games, and third-down back Kevin Faulk has been sidelined for eight weeks. Belichick has been secretive about their status this week, and it’s not clear if either will play Sunday. Patrick Pass and Heath Evans have picked up some of the slack, but this is a much better team when Dillon is on the field.

KEY TO THE GAME

These two teams will face off twice in 22 days, and the key will be the same both times: The Jets need to get their offense moving and put some points on the board. Bollinger, Martin, and Doug Jolley came through against a mediocre New Orleans defense last week. Can they perform every Sunday?

Lahman’s Pick: Patriots 24-10

slahman@nysun.com