"It was a difficult situation to be in for sure," he said.
"Maybe I was tired, I didn't feel like it was happening out there.
"It was an important start to the third set. I was able to stay in the lead and everything came back, the serve, the footwork and so on."
Breaks were always going to be at a premium in this meeting of big servers, and so it proved.
Federer's lone break won him the first set and Dimitrov reversed the act in the second.
The 17-time slam winner was letting opportunities slide, losing seven break points in the opening two sets.
The champion responded by roaring out of the gates in the third, jumping a 3-0 lead.
This was no-fuss Federer, making fewer winners but just eight unforced errors for the set.
Dimitrov couldn't match the high level of consistency coming from the Federer racket and won just 14 points as he again trailed in the set count.
Federer took the ascendancy in the fourth set to Dimitrov's disgust, the world No.28 kicking the ball into the net at his lost chance.
The Bulgarian picked himself up one last time to question Federer on serve but Federer delivered an emphatic response.
The Rod Laver Arena favourite sent down two aces and a dominant smash to march on, cruising into the fourth round where he will face Belgian David Goffin.
Federer's milestone win also makes him the oldest man to reach the last 16 at Melbourne Park since Andre Agassi in 2005.
- AAP
