ESPN NFL

With rookie quarterbacks and first-year coaches, the Indianapolis Colts and Miami Dolphins were thought to be two of the NFL's bigger rebuilding projects.

Instead, they sit with surprising 4-3 records heading into a matchup that holds legitimate playoff implications Sunday in Indianapolis.

Both teams are coming off road victories that put them over .500 for the first time since 2010, though the Colts' certainly qualified as more dramatic. Andrew Luck orchestrated two 80-yard touchdown drives in Sunday's 19-13 victory at Tennessee -- one to tie the score in the fourth, and the other to win it in overtime.

The Colts have already doubled their 2011 win total, and Luck has won one more game than Peyton Manning did as a rookie. They're 3-1 since offensive coordinator Bruce Arians took over for the ailing Chuck Pagano.

"We got four more wins than everyone thought we would have, so that's good," linebacker Pat Angerer said.

Luck has thrown eight TDs and eight interceptions, posting a passer rating of 74.6 while his 281.6 passing yards per game rank ninth in the league. Indianapolis has 13 first- or second-year players on the roster, and Luck along with running back Vick Ballard and receiver T.Y. Hilton are three of the rookies providing the biggest impact.

"I think a big thing for us is realizing you are a rookie, that doesn't mean you have to play as a rookie," said Luck, who is one 300-yard passing game shy of tying Manning's NFL rookie record (four). "You don't have that excuse. This team needs us, the rookies, to perform well and perform well now, and I think guys have taken that to heart."

Ryan Tannehill has helped lead Miami to similarly surprising success in the season's first half. But his status for Sunday's game is still unknown after an early sack knocked him out of last week's 30-9 win against the Jets and left him with a bruised left knee and quadriceps muscle.

Tannehill's MRI on Monday revealed no structural damage, and he was on the field for Wednesday's practice, splitting snaps with Matt Moore.

Moore went 11 of 19 for 131 yards in New York as the Dolphins won their third-straight under rookie coach Joe Philbin. They haven't won four straight since 2008.

"It always helps having your backup come in and perform like that," running back Reggie Bush said. "Not missing a beat."

One of the league's more experienced backups, Moore threw 16 TDs and nine interceptions with an 87.1 rating in 13 games last year.

"I just prepare and know that the opportunity can come at any time," Moore said. "When you get in there, manage the game, don't turn the ball over, but at the same time take your shots and make big plays. That's just how I approach it."

Miami has been outgained in each game during its winning streak, including a jarring 825-428 disparity in the last two. A running game that ranks 11th in the league (115.9 yards per game) has all but disappeared, averaging 71.8 over the last four. Bush hasn't run for 60 yards or more since Sept. 30.

Indianapolis is 24th in scoring (19.4 ppg) despite ranking eighth in total offense (373.0 ypg). That inefficiency is largely due to 13 turnovers and the offense only scoring touchdowns on 45.8 percent of its red-zone possessions -- 24th in the NFL.

"It's great to have a winning record. It's much better where we are now than 3-4 or 2-5," Luck said. "We realize we have so much more to improve on in every game. We're not overlooking any opponent by any means. We haven't earned that right. I don't think we'll ever earn that right."

Luck will be without one of his red-zone targets on Sunday, as rookie tight end Coby Fleener won't play after suffering a shoulder injury against the Titans.

He might also be without running back Donald Brown, who was downgraded to questionable Saturday with a knee injury. Should Brown not be able to go, Ballard would start.

Additionally, the Colts will be missing a member of their secondary with whom the Dolphins are familiar. Miami dealt cornerback Vontae Davis to Indianapolis for two draft picks late in the preseason, but Davis won't face his former team due to a knee injury.

The Colts have won the series' last three games, all with Manning under center.