Then, the second half happened.
There was a considerable amount more pressure in Tannehill's face, and the offense got away from the running game, which both proved to be the difference in Miami's momentum in the two halves.
The Dolphins and the Colts both looked like AFL teams in the first half on Sunday, but the tone of the game changed drastically in the final 30 minutes of regulation.
The offenses put up 30 points in the first half to just 13 in the second half, with the Colts presiding over 10 of those points.
After starting off red-hot going 10-for-14 passing (71.4 percent) for 158 yards (11.3 YPA) and a touchdown, Tannehill went 12-for-24 (50 percent) for 132 yards (5.5 YPA) in the second half. The Colts blitzed less (10 times in the first half, seven times in the second), but got far more pressure (three in the first half, seven times in the second half).
Still, there were some miscues by the Dolphins that resulted in pressure on Tannehill.
Left tackle Jake Long gave up a sack-fumble to Colts linebacker Dwight Freeney. Luckily for Long and the Dolphins, the left tackle recovered the fumble and rumbled forward for two yards.
The Dolphins would not always be so fortunate, though.
At the end of the first half, the Dolphins completely whiffed on Freeney, allowing him to come through unblocked for a clean hit on Tannehill, which nearly resulted in another fumble were it not for the Tuck Rule.
The Colts got some early pressure on Tannehill, but the rookie had a comfortable pocket for much of the early going. The Dolphins did what they could to counter any pressure the Colts might have gotten with the short and intermediate passing game.
The second-half struggles weren't about just the passing game, though. After running 12 times for 61 yards in the first half, the Dolphins ran the ball just six times for 23 yards in the second half.
Put that up against their 24 second-half pass attempts, and while execution is part of the problem, so was play-calling.
The Dolphins are guilty of much the same thing the Bills are, except instead of giving up on the running game against a good run defense while trailing, the Dolphins gave up on the running game against a bad defense while leading.
The Dolphins ran several running plays to the outside that consistently picked up positive yards in the first half, including a 20-yard pitch play to running back Daniel Thomas, and of course, Reggie Bush's sensational 18-yard touchdown run.
These plays were effective because of the speed of the Dolphins backs, as well as some good downfield blocking by the Dolphins offensive line.
Where does the blame lie for the offense's tailspin in the second half?
Not counting a kneeldown to end the first half, the Dolphins ran the ball six times to the outside and five times up the middle. In the second half, the Dolphins ran the ball two times to the outside and four times up the middle.
The Dolphins learned quite a bit about themselves in this game. They need to stick with the running game, and while Tannehill remains a great quarterback against pressure, they can't afford to let him have consistent pressure in his face if they want to maintain offensive rhythm.
Going forward, look for the Dolphins to get back to what worked for their offense early this season, when they were able to use the running game to buy time for Tannehill in the pocket.
If they're able to do that, the offense could realize the potential we saw from it in the first half against the Colts on a more consistent basis.
Erik Frenz is the AFC East lead blogger for Bleacher Report. Be sure to follow Erik on Twitter and "like" the AFC East blog on Facebook to keep up with all the updates. Unless specified otherwise, all quotes are obtained firsthand or via team press releases.