During their 21-year existence, the Baltimore Ravens have been beaten by 30 of the other 31 franchises in the NFL.

The only team that has failed to upend the Ravens: the Cowboys, who play host to Baltimore on Sunday. The Ravens are 4-0 against the Cowboys, and each victory has been a significant one for Baltimore.

In 2000, the Ravens shut out Troy Aikman and the Cowboys, 27-0, for their fourth shutout of the season. The Baltimore Sun headline said it all: Big D runs into bigger 'D.'

In 2004, Baltimore routed Dallas again, beating the Cowboys, 30-10 behind Kyle Boller's two touchdown passes. The Ravens improved to 7-3, their best start in team history.

In 2008, the Ravens ruined the farewell party by knocking off the Cowboys in the final game at Texas Stadium. In the final four minutes, Willis McGahee ran 77 yards for a touchdown and Le'Ron McClain broke free for an 82-yard score.

In 2012, Baltimore edged Dallas, 31-29, in what became a costly victory. Ray Lewis tore his triceps, an injury many believed would be season-ending. Three months later, Lewis returned for his "last ride" and helped the Ravens to their second Super Bowl title.

Coach John Harbaugh was asked whether he would mention to his players that the Cowboys are the only team never to beat the Ravens.

"No, probably not," Harbaugh said. "Is that true? How many games have there been?"

Harbaugh was informed that the Ravens have won all four meetings with Dallas.

"Does that count in this year’s standings?," Harbaugh asked with a smile. "Does that help us in any way? No. So, we need to be 1-0 against them this year. That is the goal: 1-0 against them this year."

The last time Dallas defeated a Baltimore team was Dec. 6, 1981, when the Colts lost to the Cowboys, 37-13, at Memorial Stadium. Tony Dorsett ran for 175 yards, and Ron Springs scored three touchdowns.

Here are six players to watch, courtesy of ESPN Cowboys reporter Todd Archer:

OFFENSE

Cowboys quarterback Dak Prescott has passed for 14 touchdowns and two interceptions this season. Justin K. Aller/Getty Images

QB Dak Prescott: For the first time this season, Tony Romo will be active as the Cowboys’ backup. Will Prescott change his ways knowing the franchise’s all-time leading passer is on the sidelines? The Cowboys don’t believe so. Prescott doesn’t believe so. What has made Prescott special is that he can have bad drives, bad quarters or bad throws but make it all come together eventually. That’s not something you see from a rookie very often. He is helped by the talent around him, but he is making the plays that matter most.

RB Ezekiel Elliott: Jason Garrett likes to say the runner matters. Elliott deserves to be in the MVP talk for what he has done for what is now the team with the best record in the NFL. He can run by defenders. He can run over defenders. He can pick up the blitz. He can catch passes out of the backfield. The Ravens offer a stiff test, but the Cowboys have been able to solve the riddle of every run defense so far this season.

WR Cole Beasley: He leads the Cowboys in catches and has four touchdown catches. He is a mismatch for just about any defense. His top trait is his quickness. He can create separation early in a route, creating easier throws for Prescott. If teams want to pay extra attention to Dez Bryant, then Beasley can hurt defenses, especially on third down.

DEFENSE

DE DeMarcus Lawrence: He led the Cowboys in sacks last season with eight, and missed the first four games this season because of a suspension. He had his first sack of the season last week against Pittsburgh, and had a big tackle for loss as well. Lawrence gets his sacks in bunches. He had a sack in two playoff games in 2014. He had a sack in seven straight games last season. The Cowboys hope he is about to start another hot streak, because they need to get more out of their pass rush.

CB Brandon Carr: After lining up exclusively at left cornerback in his first four years with the Cowboys, he was moved to the right side this season and has flourished. He has one interception, but he has been a much more physical presence than in year’s past and playing with confidence. He has been in position to make plays and mostly made them. Speedy receivers give him some trouble, but he has been a sure tackler when a receiver has made a catch in front of him.

FS Byron Jones: He has focused all of his attention at safety this season after splitting time between cornerback and safety a year ago as a rookie. He has been what the Cowboys had hoped with his ability to play the deep balls. He has been a good tackler as well. He is still looking for his first interception, but he is in the right spots. His ability to play cornerback, however, might help this week if Orlando Scandrick can’t play. Jones was a slot cornerback last season and has a good feel for leverage and help playing inside.