Garcia said he "finally felt like I knew what I was doing out there" after firing a three-under 68 that gave the 33-year-old Spaniard a three-over aggregate of 216.
Harrington, though, was unable to arrest his recent form slide as he plunged to a 77 for 225.
Asked by reporters what it felt like to be put on the clock by officials, Garcia replied: "I felt like I was rushing quite a lot. I even played out of position when it wasn't my turn, probably two or three times, to try to catch up.
"But it's difficult when it's this breezy," he said of winds that were gusting up to 15 mph. "If you're not hitting the ball well you have to think of so many things.
"With shots from the rough you have to realise where you want to fly it, how much it's going to roll, take care of whichever bunker is around. It all takes a little bit more time to figure out.
"It's difficult when you're on the clock (but) I think we tried as hard as we could, both of us, and we managed to get back on time."
Harrington beat Garcia in a play-off to win The Open at Carnoustie in 2007 and there has been talk of friction between the European Ryder Cup pair over the years.
Asked to describe his relationship with the Irishman, world number 15 Garcia replied: "Good, yeah, normal. I think we both respect each other.
"We seemed to be a little bit slow out there today but other than that it was fine," added the gifted Spaniard who is still searching for his first Major victory.
Harrington could find no inspiration on Saturday and went 18 holes without a birdie.
"I didn't play very well so that wasn't much fun," said the triple Major winner. "But he played very well and you've got to think he was quite unlucky to only shoot three-under.
"I don't think I've made enough birdies in the last six weeks. If I hit it close I miss the putt, if I hit a nice iron shot it doesn't seem to go close.
"It's just the nature of the game. When it turns it will seem easy. I won't look back and I won't remember this run for sure," added world number 73 Harrington.
"It will be long forgotten when it does turn around and that's the nature of the game."
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