MIAMI -- Dolphins fans have witnessed a bunch of exasperating things this season: Ryan Tannehill underthrowing or overthrowing Mike Wallace, the offensive line being beaten for sacks, the running game being stuffed in a handful of games.
But here's one thing they haven't seen: Opposing receivers beating Dolphins defensive backs deep for touchdowns.
And that's a testament to the play of the team's top four cornerbacks, who are all allowing less than a 70 passer rating in their coverage area.
To put that in perspective, of the 112 cornerbacks who have played at least a quarter of their team's snaps, only 22 are below 70 in that category.
And Miami is the only team with four of those 22, according to Pro Football Focus.
The Dolphins have allowed only one touchdown reception by an opposing receiver -- a 14-yard pass from Tom Brady to Aaron Dobson, against Nolan Carroll.
"That's cool," said cornerback Brent Grimes, who has had an exceptional season. "With the talented receivers in the league, that's a good accomplishment."
That needs to continue in Pittsburgh on Sunday, when the Dolphins face Antonio Brown, who had six touchdowns and 1,103 receiving yards on a league-high 85 catches, and Emmanuel Sanders, who has 54 receptions, 604 yards and four touchdowns.
Grimes hasn't been beaten for a touchdown all season, and quarterbacks have a 62.6 rating in his coverage area -- best among cornerbacks with at least 700 snaps. (Grimes has played 853.)
"A lot of times unless you are just isolating on him, you don't realize how good of a job he is doing on some of these receivers," defensive coordinator Kevin Coyle said. "He's something else."
Grimes has four interceptions and seldom drops a ball he gets his hands on.
"He's a phenomenal athlete, and he has incredible eye-hand coordination," Coyle said. "I think he sleeps with the football. Really, as soon as he walks out on the practice field, you see him every day, he's got a ball in his hands during stretching.
"He's flipping it around. He's catching it. He's kicking it. He's a ball of energy. He makes some catches that he makes look so easy in practice at times."
While Grimes has set the tone, the Dolphins' other cornerbacks also have delivered some of the best work of their careers.
Patterson, who is questionable for Sunday with a groin injury that has limited him to five games this season, is allowing just a 36.1 rating in his coverage area (second-best in the league) and leads the league in interceptions-per-snap (four in 229).
And Nolan Carroll and Jimmy Wilson have made "tremendous improvement," according to receiver Rishard Matthews, who has battled both in practice the past two seasons.
Carroll has allowed only 47.7 percent passes thrown against him to be completed, compared with 57 percent last season, according to Pro Football Focus. Wilson has made very few significant mistakes in coverage.
"They're doing a better job," coach Joe Philbin said of Carroll and Wilson.
And the group of cornerbacks overall have "been very sound from an assignment standpoint," Philbin said. "We haven't seen, knock on wood, a lot of blown coverages."
Depending on the pass rush, Dolphins defensive backs might need to stick to their man a bit longer Sunday because of Steelers quarterback Ben Roethlisberger's improvisational skills.
"He does a great job of extending a play but still look downfield and find a guy at maybe the last second," Philbin said. "He's this far from crossing the line, and all of the sudden he locates the receiver and puts the ball on them."
The Dolphins have had less success keeping tight ends out of the end zone than receivers, but the team's coverage against tight ends has improved markedly since a horrible start.
Over the first four games, the Dolphins allowed six touchdowns against tight ends.
In the eight games since, Miami has allowed two: to San Diego's Antonio Gates and a 1-yard game-winner to Carolina's Greg Olsen.
And this is encouraging: The Dolphins have allowed fewer than 52 receiving yards by tight ends in seven of their past eight games.
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