The Giallorossi looked on course for victory against Sassuolo after Alessandro Longhi's own goal had put Roma ahead in the 19th minute.
Domenico Berardi popped up deep in injury time to earn the away side a point at the Stadio Olimpico.
"If you don't score the second goal then what happened to us can occur," Garcia said to Corriere dello Sport. "We are all disappointed because when you lose two points a few seconds away from the end it's frustrating.
"But I have no doubt regarding my team's capacity.
"The important thing was that we played well.
"We have to be calm because despite the setback, we still lead the standings."
The result followed Roma's 1-1 draw at Torino and saw their lead at the top of the Serie A table cut to one point after Juventus climbed to second with a 3-0 win over Napoli.
The Giallorossi are unbeaten this season and host Cagliari after the international break.