INDIANAPOLIS -- To Colts fans, Sunday's 21-13 loss to the Miami Dolphins was a disappointment. Fans grumbled as they left the RCA Dome. They watched the Colts fall behind, 21-3, in the first half. Too many times last season, they saw the same thing.

But the Colts defense is a unit under construction. The encouraging news is that last year's defense, which surrendered 31 points a game, would have folded and probably given up 42 points. The Colts started tightening up as the game wore on, giving up 147 yards on 28 plays in the second half -- and no points.

If anything, the defense put the Colts in position to come back and make the game competitive. The offense let them down.

Twice in the first half, receivers let balls bounce from their hands into those of Dolphins defenders. In the third quarter, the Colts had a first down at Miami's 2-yard line. Edgerrin James had four runs; and gained no yards.

"I'd give to Edgerrin four times," Dolphins middle linebacker Zach Thomas said. "He's such a patient runner. Once you think you got him, he'll make a move as you are grabbing him."

In fact, it appeared that he scored on a third-down play from the 1. There was no conclusive replay on the scoreboard that merited coach Tony Dungy making a replay challenge. On the next play, he was stopped for a 1-yard loss, and the scoring opportunity died.

The encouraging news for the Colts is that James looks like he did before reconstructive knee surgery. He had 210 yards of total offense, rushing for 138 and catching eight passes for 82 yards. Wide receiver Marvin Harrison was unstoppable. Despite double-coverage, Harrison caught 11 passes for 144 yards and a touchdown.

"We were trying to double Marvin Harrison and he ended up with 11 catches," Dolphins coach Dave Wannstedt said. "That's incredible."

As nice as those statistics were, the Colts scored only 13 points and felt as though they left at least 11 to 14 more unscored. Critics were quick to point out that the Colts scored an average of 19 points during their losses last year.

"That was the difference in the game," Dungy said. "We went up and down the field as much as they did. They scored touchdowns with theirs. We didn't score at all at times and had to settle for field goals. We talked about it all week. You can't turn the ball over. You can't blow coverages. You can't blow things that give them easy plays."

But those problems are fixable. James still lacks breakaway speed, but that is slowly coming back. Part of the problem scoring in the red zone was the absence of tight end Marcus Pollard, who was out with a rib injury. Pollard returns next week.

"We didn't quit and we gave ourselves a chance to win," defensive end Brad Scioli said. "There's two things you can do. You can just fold and they can walk all over you. Or you can fight and come back and have a chance to win."

The Colts drove to the Dolphins' 6 with four minutes left and settled for a field goal to cut the lead to 21-13. Quarterback Peyton Manning got the ball back at his 16 with 2:15 left and drove his team to the Dolphins' 6 with two seconds left.

The final pass to Qadry Ismail was incomplete and the game was over.

The Dolphins were playing in playoff form. And while the Colts were not, there were signs they are starting to turn their fortunes around.

It was a start.

John Clayton is a senior NFL writer for ESPN.com.