Allen earned recognition as part of an offensive line that allowed the second-fewest sacks (24) in the league, behind Indianapolis who allowed just 14, and one-or-fewer sacks in nine-of-16 games. He helped lead the way as the Cowboys gained 541 total yards while giving up only one sack in 50 pass plays in his first career start at left guard at Washington on September 12. He helped lead the way as Emmitt Smith became just the third player in the last 29 games to rush for over 100 yards against the Atlanta Falcons on September 20, when he rushed for 109 yards. Allen's blocking helped the Cowboys offensive line allow only one sack in 40 pass plays in Philadelphia on October 10. He gave up no sacks to the Redskins on 32 pass plays on October 24. His blocking helped Smith to rush for 140 yards and two touchdowns in the first half as the Dallas offense recorded 205 rushing yards in Minnesota on November 8. Allen helped the Cowboys running backs record 149 yards before leaving the game in the third quarter with a sprained medial collateral ligament (MCL) in his right knee against the Packers on November 14. He missed his first career game in Arizona on November 21, snapping strings of 97 consecutive games played and 90 consecutive starts. He missed the next four games with a sprained knee. He returned to the starting lineup in New Orleans on Christmas Eve and helped the Cowboys offensive line give up no sacks on 39 pass plays while helping Smith to rush for his eighth 100-yard game of the season. In the season finale against the Giants on New Year's Day, he helped block for Smith as the latter recorded his ninth 100-yard game of the season. Allen was also part of an offensive line that did not allow a sack in 33 pass plays during the game. In the NFC Wild Card Playoff Game in Minnesota on January 9, he opened holes for Smith to rush for 99 yards, including a Dallas postseason record 65-yarder.