The visitors were without first-choice quarterback Andrew Luck through injury, and his replacement Matt Hasselbeck got off to a shaky start when his first pass attempt was intercepted by Paul Worrilow.
Hasselbeck's mistake was not to prove costly as Matt Bryant's 46-yard field goal hit the upright, but the Colts gifted possession straight back to their hosts when Worrilow recovered a Frank Gore fumble.
The first points of the contest finally arrived right at the end of the opening quarter, and it was the hosts who got them as Ryan found DiMarco wide open in the endzone for a 15-yard score.
The same two players combined again to double Atlanta's advantage, with Ryan this time picking out DiMarco from a yard to put the hosts in control.
They couldn't claw any more of the deficit back before half time, however, as they entered the break trailing by seven.