Only Martina Navratilova (306) stands in front of him.
"It's very exciting, I must tell you," said Federer of the milestone. "Like when I reached 1,000 [tour-level wins] last year, it was a big deal for me. Not something I ever aimed for or looked for, but when it happens, it's very special. You look deeper into it, I guess, where it's all happened and how. So it's very nice. I'm very happy."
The 48-minute first set went in Federer’s favour behind a service break at 3-all, the only interruption the opening, then closing, of Rod Laver Arena’s retractable roof due to rain. But the Bulgarian Dimitrov, who after three straight-sets losses took his first set off Federer in the Brisbane quarter-finals earlier this month, would get another to level the match at a set apiece, his aggressive play paying dividends against the 17-time Slam champ.
Federer didn’t wait long to assert himself in the third set, breaks coming in the second and sixth games for a 5-1 advantage. A game later he was ahead two sets to one. A forehand error from Dimitrov at 2-all, 30/40 in the fourth and final set would give Federer a seemingly insurmountable lead, and the Swiss went on to clinch the contest in two hours and 40 minutes. He finished with 47 winners, including 13 aces.
"That was my goal, to react quickly after the second set because I struggled a little bit," said Federer. "But then found my way back, then was able to take charge of the match. It was important. Conditions, again, were very different indoors than they were against Dolgopolov in the second round. Even night session plays different.
"Just got to manage these conditions a bit. I'm pleased. Wasn't easy. I didn't expect it to be against Grigor. It was a tough round, so I'm happy."
It was Dimitrov's seventh straight loss to a Top-10 player.
Federer, at 34 a decade Dimitrov’s senior, is the oldest man to reach the round of 16 at the Australian Open since Andre Agassi played his way into the quarter-finals in 2005. He is looking to become only the third man to win five Australian Open singles titles after Roy Emerson (six) and Novak Djokovic (five), having won the title in 2004, 2006, 2007 and 2010.
Dimitrov was bidding to reach the fourth round for the third consecutive year. His best Australian Open result is a quarter-finals showing in 2014 (l. to Rafael Nadal).
"I felt I could have played better tennis throughout the whole match," said Dimitrov. "After the second set, I was just getting a little flat. I was hoping to have a better result. I'm not going to lie. Losses like that always hurt, but in the same time I just lately haven't played those kind of matches I think.
"Just don't get discouraged at the same time. It's not like I'm losing every match or anything like that. I thought I played good tennis at the beginning of the year, and that's important. Still a lot of tournaments to come ahead. So I'm really going to try to go out there and use all my confidence that I've built so far and, of course, keep trying."
Federer advances to play No. 15 seed David Goffin of Belgium, a 6-1, 3-6, 7-6(2), 7-5 winner over No. 19 seed Dominic Thiem of Austria. The 25-year-old Goffin is through to the fourth round of a major for the third time, having also reached the last 16 at 2012 Roland Garros (as a qualifier) and 2015 Wimbledon. The right-hander will look to overturn a 0-3 FedEx ATP Head2Head record over Federer.